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STUDIES IN NEUROLOGY

PUBLISHED BY THE JOINT COMMITTEE OF

HENRY FROWDE AND HODDER & STOUGHTON

17 WARWICK SQUARE, NEWGATE STREET,

LONDON, E.C. 4

STUDIES IN NEUROLOGY

BY

HENRY HEAD, M.D., F.R.S.

IN CONJUNCTION WITH

W. H. R. RIVERS, M.D., F.R.S. JAMES SHERREN, F.R.C.S.

GORDON HOLMES, M.D., C.M.G. THEODORE THOMPSON, M.D. GEORGE RIDDOCH, M.D.

IN TWO VOLUMES VOL. I

LONDON HENRY FROWDE HODDER & STOUGHTON, LTD.

OXFORD UNIVERSITY PRESS WARWICK SQUARE, B.C. 4

I92O

PRINTED IN GREAT BRITAIN BY RICHARD CLAY AND SONS, LTD., 3RUNSWICK STREET, STAMKORD STREET, S.E. 1, AND BUNGAY, SUFFOLK.

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PREFACE

THESE volumes consist mainly of a re-publication of the following papers—

" The Afferent Nervous System from a New Aspect," by Henry Head,

W. H. R. Rivers and James Sherren (Brain, 1905, vol. xxviii. pp.

99-116). " The Consequences of Injury to the Peripheral Nerves in Man," by

Henry Head and James Sherren (Brain, 1905, vol. xxviii. pp. 116-340). " A Human Experiment in Nerve Division," by W. H. R. Rivers and

Henry Head (Brain, 1908, vol. xxxi. pp. 323-450). " The Grouping of Afferent Impulses within the Spinal Cord," by Henry

Head and Theodore Thompson (Brain, 1906, vol. xxix. pp. 537-741). " The Automatic Bladder, Excessive Sweating and Some Other Reflex

Conditions, in Gross Injuries of the Spinal Cord," by Henry Head

and George Riddoch (Brain, 1917, vol. xl. pp. 188-263). " Sensory Disturbances from Cerebral Lesions," by Henry Head and

Gordon Holmes (Brain, 1911-12, vol. xxxiv. pp. 102-271). "Sensation and the Cerebral Cortex," by Henry Head (Brain, 1918,

vol. xli. pp. 57-253).

It was thought better to make no material change in their arrangement ; for each of them deals with a definite theme and is concerned with some distinct aspect of the functions of the nervous system.

Each of these papers contained a short account of the methods employed in testing sensation ; these I have excised and written a fresh chapter in which they are combined. I have also added an Introduction and an Epilogue dealing with the common aims which underlie these various researches.

Finally, some of the. most serious criticisms of our researches on the functions of the peripheral nervous system have been considered in an Appendix at the end of the second volume.

I cannot close this short preface without expressing my thanks to all those who have collaborated with me. Without their help, so generously given, this work could not have been brought to a successful termination.

H. H.

308410

CONTENTS PART I— INTRODUCTION AND METHODS OF EXAMINATION

CHAP. PAGE

I. INTRODUCTION ............ 3

II. METHODS OF EXAMINING SENSATION . .12

(A) Spontaneous Sensations ......... 14

(B) Loss of Sensation . . . . . . . . . . 15

(1) Touch .15

(a) Light Touch 15

(6) Pressure Touch . . . . . . . .17

(2) Pain 18

(a) Superficial Pain . . . . . . . . .18

(6) Pressure Pain .19

(3) Temperature 21

(4) Roughness 23

(5) Tickling and Scraping ......... 24

(6) Vibration 24

(7) Localisation ........... 25

(8) The Compass Test 26

(a) Simultaneous Application of Two Points ..... 26

(6) Successive Application of Two Points ..... 29

(9) Position . 30

(10) Passive Movement .......... 30

(11) Appreciation of Weight ......... 32

(a) With the Hand Supported 32

(6) With the Hands Unsupported . . . . .33

(12) Appreciation of Size ......... 33

(13) Appreciation of Shape in Two Dimensions ..... 33

(14) Appreciation of Form in Three Dimensions ..... 33

(15) Appreciation of Differences in Texture ...... 34

III. CLINICAL APPLICATION OF THESE METHODS ....... 35

(1) With Lesions of the Peripheral Nervous System ..... 35

(2) With Lesions of the Spinal Cord, Bulb, and Mid-Brain .... 39

(3) With Cerebral Lesions . . . . . 46

PART II— THE PERIPHERAL NERVOUS SYSTEM

THE AFFERENT NERVOUS SYSTEM FROM A NEW ASPECT . . 55

THE CONSEQUENCES OF INJURY TO THE PERIPHERAL NERVES

OF MAN . . . .66

I. NERVE SUPPLY OF THE PALM OF THE HAND 68

§ 1. Division of the Ulnar Nerve . . V . . . . . .68

§ 2. Variation in the Extent of the Area supplied by the Ulnar Nerve . . 70 § 3. Loss of Sensation produced by Division of the Ulnar Nerve, when its Dorsal

Branch remains intact ......... 73

§ 4. Division of the Median Nerve . . . . . • . . .75

vii

viii CONTENTS

CHAP. PAGE

§ 5. Variation in the Extent of the Area supplied by the Median Nerve 76

§ 6. Division of both Median and Ulnar Nerves ...... 78

II. RECOVERY or SENSATION AFTER DIVISION OF THE NERVES OF THE HAND . 81 § 1. General Statement of the Phenomena of Recovery . . . .81

§ 2. Recovery after Division of Particular Nerves .... 87

(A) Median Nerve ......... 88

(B) Ulnar Nerve . . . 92

(C) Median and Ulnar Nerves ....... 96

(D) Summary . . i 97

III. RECOVERY OF SENSATION AFTER INCOMPLETE DIVISION OF THE NERVES OF THE

HAND .99

IV. NERVE SUPPLY OF THE FOREARM . . . . . . . • . 106

§ 1. The Post-axial Half of the Forearm . . . . . .107

§ 2. The Pre-axial Half of the Forearm 108

V. INJURIES TO THE BRACHTAL PLEXUS 115

VI. Loss OF SENSATION IN THE ARM FROM DIVISION OF POSTERIOR NERVE ROOTS . . 122

VII. NERVE SUPPLY OF THE LOWER LIMB 126

§ 1. The Sole of the Foot 126

§ 2. Loss of Sensation produced by Injury to the Nerves of the Leg . : . 128

§ 3. The Nerve Supply of the Leg deduced from Residual Sensibility . . 133

VIII. DEEP SENSIBILITY , . . . . . . 137

IX. SENSATIONS OF HEAT AND COLD . 144

X. THE COMPASS TEST .-;- . . 148

XI. SENSIBILITY OF THE HAIRS 156

XII. HYPERALGESIA 160

XIII. CHANGES IN THE SKIN ASSOCIATED WITH INJURIES TO PERIPHERAL NERVES . . 165

XIV. CHANGES IN THE NAILS ASSOCIATED WITH NERVE INJURIES . . . .175 XV. PARALYSIS AND OTHER MUSCULAR CHANGES 184

XVI. THEORETICAL . . . 189

DESCRIPTION OF SOME ILLUSTRATIVE CASES 201

A HUMAN EXPERIMENT IN NERVE DIVISION

I. HISTORY OF THE CASE m . ' . . . 225

II. CONDITIONS OF EXAMINATION . . . . . . . . . . 242

III. THE PHENOMENA OF DEEP SENSIBILITY . . . . . . . . 246

IV. PROTOPATHIC SENSIBILITY ..... 257

§ 1. Borders of Dissociated Sensibility . 257

§ 2. Pain 258

§ 3. Heat and Cold ........... 261

§ 4. Hair Sensibility ........ 272

§ 5. The Sensibility of the Glans Penis 274

V. EPICRITIC SENSIBILITY ..... 278

§ 1. Tactile Sensibility . 278

§ 2. Thermal Sensibility 280

§ 3. The Compass Test 283

§ 4. The Sensibility of the Triangle ... . 285

CONTENTS ix

CHAP. PAGE

VI. TROPHIC, VASOMOTOK, AND PILOMOTOR CHANGES . . . . . 288

§ 1. Vasomotor and Trophic Disturbances of the Skin . . 288

§ 2. The Pilomotor Reflex .289

VII. ADAPTATION TO HEAT AND COLD . . . .'.>... . . 292

VIII. LOCALISATION AND SPACIAL DISCRIMINATION ... . 296

IX. INTENSITY . 306

X. PUNCTATE SENSIBILITY .312

§ 1. Heat- and Cold-Spots . . , . .313

§ 2. Pain-Spots '" . '. . 316

§ 3. Touch-Spots .... .319

XI. GENERAL THEORETICAL CONCLUSIONS 324

§ 1. The Integration of Afferent Impulses . . . . . . 324

§ 2. Sensory and Non-Sensory Afferent Impulses . . .-'.'. . 327

PART I

INTRODUCTION AND METHODS OF EXAMINATION

VOL. I.

CHAPTER I

INTRODUCTION

Tins book contains a series of researches into the physiology of the nervous system based on clinical observations. Each section of the work formed the subject of a separate communication published at various times in Brain; but they have been rearranged so as to comprise an orderly sequence extending from the peripheral nervous system to the receptive centres of the cortex.

Throughout the last eighteen years, occupied by these investigations, I have had the inestimable advantage of collaborating with fellow -workers each of whom was an expert in his own aspect of the subject. Any one who compares the various portions of this book will recognise how greatly the work has gained by this diversity of outlook, and I cannot be sufficiently grateful to my colleagues for all they have taught me. Our observations must of necessity contain errors ; but these would have been many times more numerous if I had not had the assistance of their expert knowledge.

But in spite of the diversity of outlook evident in each section of this book, certain basic principles guided us throughout and served to weld its various portions into a coherent whole. These may be summarised under the following headings.

1. The Tests employed must yield Measurable Results,

Throughout we have attempted to employ tests which yielded measurable results. In the case of the experiment on my arm this presented no difficulty ; we adopted, with certain modifications, the methods already in current use in the psychological laboratory. For we were not hampered by lack of time or opportunity. A set of observations which failed on one day could be repeated on some subsequent occasion, and multiplied almost to any extent. We were not compelled to consider the wishes of the patient, and had no solicitude as to his good will.

As the outcome of these elaborate experiments on my arm and with the gradual progress of our knowledge we were able to evolve a series of tests applicable to the less favourable conditions of clinical research. These are described fully in Chapter II.

The results of these tests could be expressed in measured terms; we eliminated as far as possible uncorroborated opinion. But no such measure- ments in pathological states can be of any value without some comparable

4 STUDIES IN NEUROLOGY

normal standard. It is impossible to apply to any individual patient the average data obtained by observations on healthy human beings, however numerous. If the abnormal measurements are to be of any value they must be compared with records of the same tests applied to normal parts of the patient himself.

Suppose, for example, that the sensibility of the right hand is affected; all the recorded measurements must be compared with those obtained from similar portions of the left hand. But if we attempt to work out on the normal hand the exact point at which any test can be appreciated, the patient's attention is exhausted before we come to the affected parts. In most cases it is impossible to work out a true sensory threshold even over normal areas of the body under the conditions of time and opportunity yielded by clinical medicine.

We have, therefore, adopted the following relative standard of comparison. A stimulus is selected which we know to be considerably above the normal threshold for the particular part of the body under examination. This can be appreciated without fail provided the patient possesses the usual intelligence and goodwill. On applying the same test to the affected parts, it may reveal more or less gross defects in sensibility ; the strength of the stimulus is then gradually increased until either a threshold is revealed or no series of correct answers can be elicited by any stimulus applicable within the conditions of examination.

Let us take as an example of this method the use of the tactile hairs. We know from experience that contact with a hair exerting a force of 21 grm./mm.2 (5 grm./mm.) is above the threshold for the tips of the fingers in most persons. On the normal hand a series of such stimuli should lead to a perfect set of answers ; - this can be rapidly determined in any patient under examination, and we then proceed to test with the same stimulus equivalent parts on the affected side. If the answers are defective the strength of the stimulus is increased by selecting hairs of greater bending strain until each contact is appreciated. It may be that this condition is not reached until the test-hair exercises a pressure of 70 grm./mm.2; we then know that stimuli of this strength are necessary to evoke a constant series of answers over the affected parts, although the normal hand is sensitive to a hair of 21 grm./mm.2

We make no attempt to obtain an absolute threshold on the normal side ; we establish a relative difference in sensibility, and so avoid the long and wearisome procedure necessary for a strict psycho -physical determination.

An exactly analogous procedure is adopted for measuring the appreciation of passive movements or the power of discriminating the two compass points. We choose a stimulus which is demonstrably super-normal in each individual patient. Then we determine by how many times its strength must be increased to evoke a series of correct answers over affected parts. Sometimes this is not possible, because the replies remain imperfect even with the higher degree of stimulation compatible with the special conditions demanded by

INTRODUCTION 5

the test. In such a case the defective sensibility of the abnormal parts to the strongest suitable stimulation is still more evident, and we record that no threshold could be obtained.

The results of all sensory testing depend greatly on personal factors in the observer. We endeavoured to obviate this source of error as far as possible by sharing the various examinations between us. In cases of injury to peripheral nerves or spinal cord the patient was tested by each of us in turn ; with lesions of the higher centres we took notes and examined alternately.

2. The Results of our Observations are recorded in Terms of the Tests

employed.

In every instance we report the results obtained by sensory examination in terms of the tests we have employed. Such expressions as " joint sense," "muscle sense," " bathyeesthesia," " stereognosis," are strictly avoided; " deep sensibility " has been used as a general heading only to cover several different qualities of sensation arising in subcutaneous tissues, each of which is recorded under some particular test.

Failure to adopt this principle leads to infinite confusion. For, owing to the regrouping of afferent impulses on their way from the periphery to the higher receptive centres, no one of these expressions can have the same significance at different sensory levels. Thus the term " deep sensibility," as commonly used, differs profoundly with lesions in various parts of the nervous system. A peripheral injury which destroys all the cutaneous branches to any part of the body leaves " deep sensibility " intact. The patient not only recognises the posture of segments of the limb and the vibrations of a tuning-fork, but he can appreciate the tactile and painful aspects of pressure; moreover, he can localise with accuracy the position of the stimulated spot.

If the lesion is situated in the posterior columns of the spinal cord " deep sensibility " is also said to be affected; but the qualities which are lost under these conditions do not correspond to the varieties of sensation which remain intact after the destruction of the nerves to the skin. The patient, it is true, has lost the power of recognising posture, passive movement and vibration, but retains complete appreciation of touch and pain, however evoked.

Even such terms as "thermal anaesthesia" should be avoided when reporting clinical observations. For, although lesions of the spinal cord may disturb the appreciation of heat or of cold independently of one another, this is not possible with lesions of the peripheral nervous system. Here response to the grosser thermal stimuli depends on the heat- and cold-spots, punctate end-organs which react in a strictly specific manner. These minute sensitive areas are scattered irregularly over the surface of the body, but cannot be affected independently by any injury to peripheral nerves. Dissociation, when it occurs at this level, consists of a separation of the cruder,

6 STUDIES IN NEUROLOGY

more primitive aspects of thermal sensibility from the higher forms on which depend adaptation and the power of discriminating intermediate degrees of heat and cold.

Not one of the descriptive terms for disordered sensation commonly used in clinical reports is free from this ambiguity. Every loss of sensibility must, therefore, be recorded as a function of the test employed; "light touch" gives place to the results obtained with " tactile " and " pressure " hairs, or some similar means of measurement. For " analgesia " we substitute the readings of the algesimeter (" measured prick ") cr the algometer (" painful pressure "). We do not speak of " loss of thermal sensibility," but report the patient's capacity to react to the more extreme degrees of heat or of cold, and his power of discriminating intermediate temperatures. Similar rules apply to the recognition of measured movement, the compass test and " spot find- ing " ; all such expressions as " topognosis " and " perception of posture and space " must be strenuously avoided.

All our observations were recorded in terms of the tests employed ; and it was this method alone which enabled us to study the integrative trans- formations to which afferent impulses are subjected on their way from the peripheral end-organs to the highest receptive centres.

3. The Cases selected for Intensive Examination must be chosen for their

Illustrative Value.

Throughout this work we have been occupied with disorders of function, and more particularly with the study of changes in sensation. This cannot be carried out by experiments on animals, in whom it is not possible to obtain any but the crudest sensory reactions.

On the other hand, in man the lesion is not under our control, and the finest examples of functional dissociation occur in otherwise healthy persons ; the extent and nature of the structural changes cannot be determined anatomic- ally. In most of the cases where a complete post-mortem examination could be carried out the patient had died from some diffuse injury or progressive disease and, since loss of function always exceeds anatomical destruction, the microscopical picture is no accurate reflexion of the nature and distribution of the sensory disturbance. Moreover, such patients are unsuited for elaborate psycho-physical examination by the very nature of their malady.

We have been guided, therefore, by the following principles in the selection of our cases. For intensive examination we chose those patients in whom the lesion is either stationary or in process of recovery ; they must be willing, intelligent, not addicted to alcohol in excess, or subject to epileptiform seizures. We were also influenced in our choice by the illustrative value of the disturbances in function. For example, in cases of Brown-Sequard paralysis we selected more particularly those patients in whom the spacial aspects of sensation were disturbed in one extremity, whilst the qualitative loss was confined to the opposite limb; this enabled us to study the two forms of

INTRODUCTION 7

sensibility in uncomplicated dissociation. Similar principles guided our choice in examples of cortical and subcortical lesions.

After this laborious analysis of disordered function in patients with some stable lesion, we were able to interpret the less satisfactory observations which were alone possible in those who suffered from some progressive or paroxysmal affection.

Careful selection of the examples subjected to intensive study and this dual attitude towards the clinical material at our disposal is necessary before we can hope to discover the meaning of disordered functions in the nervous system.

4. The Importance of Residual Sensibility.

Sherrington (108) first introduced a valuable means of investigating sensa- tion, known as the method of " Residual Sensibility." When he wanted to determine the extent of skin supplied from the fourth thoracic root he destroyed several roots above and several below, whilst the fourth remained intact. This left a sensitive area in the centre of a zone of anaesthesia ; every part that received its innervation, however slightly, from the fourth thoracic was marked out by residual sensibility.

The value of this method and its universal importance has been strangely overlooked by neurologists. They continue to publish reports in which the extent of the analgesia is solemnly discussed ; but they do not seem to recognise the importance of considering what parts still retain their sensibility. Suppose the seventh and eighth cervical and first thoracic roots have been destroyed in man ; certain portions of the upper extremity become insensitive to prick. But when we have carefully determined the extent of the analgesia we are not justified in assuming that it represents the full supply of the divided nerve roots ; the area of sensory loss corresponds solely to those parts of the limb which they innervate exclusively. On the other hand, the upper or head- ward border of the loss of sensation corresponds to the lower limits of the sixth cervical root, which is intact ; similarly the post-axial limits of the analgesia mark out the upper limits of the second thoracic. It is not the analgesia, but the extent of the residual sensibility that is significant in such a case.

The same principle applies to the loss of sensation produced by lesions of the spinal cord. All the diagrams constructed to show sensory segmentation are built up on the study of analgesia ; in each case the borders are carefully determined and transferred to a chart as the limits of the highest segment affected. In reality the sensory condition should be looked at from the opposite point of view ; the upper border of the analgesia corresponds to the caudal extension of the lowest unaffected portion of the spinal cord. On the other hand, the loss of sensation corresponds to those parts of the body which are exclusively supplied from below the lesion, a matter of little scientific importance.

This perverted outlook is responsible for much faulty diagnosis ; for it is more important to know what segments are still capable of exercising their

8 STUDIES IN NEUROLOGY

functions than to determine what parts are utterly cut off from the sensory receptive centres. Loss of sensation represents the negative aspect of the picture, whilst residual sensibility corresponds to the functions of adjacent but intact nerve structures.

5. The Negative and Positive Aspects of a Lesion of the Nervous System.

Fifty years ago Hughlings Jackson pointed out that most lesions of the nervous system produced both negative and positive effects ; there is not -only a loss of function, expressing the destructive activity of the process, but positive symptoms appear owing to release of lower centres from control. This law was accepted as an explanation of certain individual conditions, such as the spasticity accompanying hemiplegia, but was not generally applied to the phenomena of disease.

From the earliest days of our work on the peripheral nervous system we recognised that, when the skin was deprived of certain aspects of sensibility, the response to those that remained might become peculiarly vivid. Reaction to a prick was abnormal and excessive ; the patient complained that it was more painful, although measurements showed that sensibility to this form of stimulation was considerably lessened. This is not a " hyperalgesia," but a more primitive mode of reaction, normally held in check by coincident activity of a higher sensory mechanism, which has been set free to exert a more powerful influence on the ultimate afferent centres.

This conception has been combated by certain critics mainly on the ground that the conditions under which our observations were made were " patho- logical." To many physiologists a phenomenon which can be labelled " pathological " is banned to the limbo of medicine, with which they refuse to have any concern. We, on the other hand, contend that these dissocia- tions of function give the clue to the complex activities of the nervous system.

The final act of sensation can be decomposed by changing its physiological components. The form assumed by such dissociation may resemble nothing that has previously existed in the phylogenetic history of man ; or the change in function may approximate to the character of some more primitive normal activity. This is the case with high-grade protopathic sensibility and with sensations from the glans penis where a normal part of the body responds to sensory stimulation exactly like an organ endowed with deep and protopathic sensibility only.

There is not a section of this work where Jackson's law of the positive and negative consequences of a lesion does not illuminate the phenomena under discussion. But clinicians are reluctant to abandon their conceptions of "irritation" and " hyperaesthesia " ; they assume that a part of the body which reacts excessively to stimulation must be in a condition of increased sensitiveness. They cannot be persuaded to apply the doctrine of relaxed control to the problems of sensation, although they accept it as an explanation of certain exaggerated motor activities.

INTRODUCTION 9

6. The Difference between Irritation and Release from Control.

It must not be supposed that we deny the existence of true irritative phenomena. These can be studied best in cases of injury to peripheral nerves, where they form an instructive contrast to the manifestations of protopathic release.

Take such an instance as that described on p. Ill, where the anterior division of the external cutaneous nerve had been accidentally wounded in the lower part of the forearm. A considerable area became intensely tender to the point of a pin dragged lightly across the skin ; but sensation was perfect to all the measured tests for prick, light touch, heat and cold, and the compass points were discriminated with equal ease on both hands. On exploration the nerve trunk was found to be irritated by inflammatory changes and the full distribution of its fibres was revealed as an area of tenderness accompanied by no coincident sensory loss.

On the contrary, protopathic over -reaction is strictly limited to parts which have been deprived of the higher forms of sensibility ; after division of the ulnar nerve it extends no further than the borders of the loss to light touch. If the same nerve is irritated the tenderness may extend far beyond these limits and occupy all those parts of the radial palm which are innervated by pain fibres from the ulnar nerve. This is the area that remains sensitive to prick when the median has been completely divided. Protopathic over- reaction is one of the phenomena of dissociation due to removal of higher control and marks out the parts which have been robbed of their higher sensory functions. Irritative tenderness, on the contrary, may be accompanied by no loss of sensibility; it expresses the complete peripheral distribution of the nervous mechanism that has been subjected to excitation.

Excessive sweating is another phenomenon which may be due at one time to irritation, at another to release of spinal centres from higher control. After gross injury to the spinal cord outbursts of hyperidrosis may occur, which corresponds to the parts below the lesion; these are produced by an uncontrolled response to superficial, proprioceptive or visceral stimulation. On the other hand, the sweating may be an irritative manifestation evoked from the central portion of the injured cord.

Irritative phenomena can occur without any other disturbance of function; but release from control is always signalised by some coincident defect.

7. The Necessity for avoiding a priori Hypotheses in the Study of Sensory

Phenomena.

The study of the phenomena of sensation has been much hampered by a priori hypotheses. The older psychologists assumed that the immediate consequences of stimulation corresponded categorically to the various aspects of sensation. They failed to recognise that between the impact of a

10 STUDIES IN NEUROLOGY

physical stimulus and the act of sensation lay a multitude of physiological transformations which could not be discovered by introspection.

At the time when we began this work, most writers assumed that each specific quality of sensation arose from stimulation of one particular group of end-organs. The impressions so produced were supposed to be transmitted unchanged to the appropriate cortical centres, where they evoked some single aspect of sensation. Special receptive organs were postulated for tactile, painful and thermal stimuli. With the discovery of the heat- and cold-spots, and with von Frey's further development cf the doctrine of punctate sensi- bility to include touch and pain, a sensory mechanism seemed to have been found capable of satisfying the required conditions.

But our discovery of the functions of deep sensibility at once destroyed this conception of rigid parallelism between peripheral end-organs and receptive centres. For we found that many sensations, usually attributed to " light touch," arose from stimulation of subcutaneous tissues, when the skin was entirely insensitive. Pain also could be evoked in the absence of all cutaneous sensibility.

Obviously both sensations of " touch " and of " pain " could be caused by the excitation of at least two peripheral mechanisms apiece. We were not, therefore, surprised to find that in the skin itself the sensory apparatus for heat is also double ; the " heat-spots " respond, it is true, in a specific manner, but they account for one aspect of thermal sensibility only. An appreciation of minor differences in warmth and the power of adaptation to surrounding temperatures are functions of a higher afferent mechanism.

It has long been known that the cold-spots in the skin react to certain degrees of heat ; 45° C. applied strictly to one of these spots produces a definite sensation of cold. But if the same stimulus is applied over a wider area, so as to include other end-organs of a different specific reaction, the sensation is one of heat ; impulses evoked by exciting the cold-spots are inhibited in the presence of those due to coincident stimulation of the receptive mechanism for heat.

Evidently the afferent impressions produced by the action on the body of some physical force, such as heat, are not only multiform, but may be incompatible with one another. Before they can underlie a single specific aspect of sensation, they must undergo integration within the central nervous system.

Human sense organs have been developed out of the lowliest materials; their functions do not correspond exactly to any of the final categories of sensation, which are the result of innumerable physiological transformations. These changes we have attempted to follow from the periphery to the highest receptive centres. They are of entrancing interest, because they reveal the method by which the sensory functions of man have been evolved from the primitive neural activities of his humbler ancestors.

We believe that " Sensation " was originally a vague undifferentiated state,

INTRODUCTION 11

and that progress has taken place by the slow acquirement of more specific reactions. This has occurred not only in consequence of the development of sense organs of higher capacity, but, to an even greater extent, by increasingly perfect integration of afferent impulses at various sensory levels. Finally, in man sensation is a highly differentiated reaction to physiological processes which have undergone profound transformations on their way from the peripheral end-organs to the highest receptive centres.

CHAPTER II

METHODS OF EXAMINING SENSATION

THE value of our work depends in great part on the trustworthiness of the means we have employed to examine sensation. I shall therefore devote this chapter to a description of the tests we have used and the conditions under which they have been carried out.

All the observations on my arm and hand were made with the pre- cautions and safeguards customary in a psychological laboratory. The area to be explored was not extensive and time was no object; on the slightest sign of fatigue the examination was discontinued, and I was allowed a period of freedom and rest.

Such conditions are impossible clinically; and, before we set out on the researches embodied in this work, it was necessary to develop a series of tests which stood midway between the rough-and-ready examination of the clinician and the elaborate observations of the psychologist in his laboratory. Our aim was to find a set of simple tests which would yield measurable results. We were anxious to get rid of those statements of personal opinion which play so large a part in clinical records.

As far as possible, our observations were made in a quiet room, apart from the hospital ward with its distracting sights and sounds. On the rare occasions when this was impossible, owing to the difficulty in transporting the patient, his bed was carefully screened and every method adopted to secure his undivided attention. Whenever the patient was in bed the parts to be tested were exposed as little as possible. Anything that produces a " feeling of coldness," anything that causes shivering or the appearance of " goose skin," greatly diminishes the accuracy of the answers to most tests. A damp, misty or foggy day is peculiarly unfavourable for testing sensation. The most satisfactory conditions are a warm day of early summer, or a bright, cool winter morning in a well-warmed room.

It is important that the patient should be free from all visceral discomfort ; he must not be hungry or suffer from a desire to empty his bladder. The following instance shows how potently such conditions may affect the results of even the grossest sensory tests. During the examination of R. A. H. (p. 458) it was noticed that his answers became much less accurate than they had been earlier in the day ; for he failed on the right forearm in eight out of twenty attempts to tell the head from the point of a pin. He was

12

METHODS OF EXAMINING SENSATION 13

then allowed to empty his bladder, and from that time made no mistakes; his answers, which had shown much confusion, were now uniformly correct.

At first we were in the habit of blindfolding our patients ; but in some cases, especially of cerebral disease, this is liable to lead to a state of defective general attention. During the observations on my arm, I sat with my eyes closed, as I found that this produced in me the condition most favourable for sensory testing ; for I always answered more correctly to those tests which required no close introspection when I did not attempt to think of what was going on. This was also the case with many of our patients, especially those who tended to interpret their sensations, and were particu- larly anxious to do well in the examination. But, with those of a lower grade of intelligence, closing the eyes was liable to induce a condition akin to sleep, and they might even cease to give any answer, when tested over normal parts of the body.

The examination was therefore begun with the eyes closed; but, if the results showed an unexpected want of attention on the normal half of the body, it was continued with the eyes open with the parts to be tested carefully screened. This was particularly useful during examination of the lower extremities ; but it is important that the patient should not be able to see any of the manipulations of the operation or the objects with which the tests are carried out. Some patients are more comfortable when this system is adopted than if they are forced to remain for long periods with closed eyes.

Certain well-recognised rules have guided our studies. The most important of these is to obtain the good-will and interest of the patient ; for without this it cannot be hoped that the observations will be trustworthy. When attention begins to flag, or the patient to tire, it is necessary to interrupt the examina- tion ; for this reason we arrange that the tests demanding the greatest effort and concentration should be made early in the sitting, and the coarser and subjectively easier tests reserved till the later stages of the examination.

In the second place, we have always avoided anything that might, on the one hand, suggest a response, or, on the other, confuse it. Each test was first explained to the patient, and he was allowed to watch it in action on the normal side. Then his eyes were closed or the part was screened, and the examination was begun seriously.

He was requested to reply " Yes " or to give some other simple answer appropriate to the mode of stimulation. For example, with the compass points he said " one," " two," or perhaps " I don't know " ; with the test for the appreciation of passive movement his replies were " up," " down," or " bending " and " straightening." No questions were asked during the examination. It is most important to avoid all inquiries, such as, " Did you feel that? " " Did I prick you? " " Was that one or two points? " or " Did I move your finger ? " etc. Once certain that the patient understands the nature of the test, the observer must remain absolutely silent till the examination is over. Then he may ask questions as to what the patient

14 STUDIES IN NEUROLOGY

thinks about his sensations and the difference between normal and abnormal parts. In many cases it is necessary to obtain an introspective description" or analysis of the sensations evoked; but we have attempted to keep this portion of our notes strictly separate from the records obtained with the various measurable tests.

Our aim has been to employ a series of tests which give measurable results without at the same time exhausting the patient, or demanding any but the smallest amount of introspection. The measurements so obtained are not compared with an absolute standard, but with the results yielded by the same tests on the normal half of the patient under identical conditions. Even on the normal side we do not attempt, in most instances, to discover the true threshold. We begin each series of observations on the unaffected half of the body with a test near the threshold value, but well within the patient's capacity. The abnormal parts are then examined with the same test, and, if a perfect series of answers cannot be obtained, the stimulus is increased until a threshold is reached, or, if this is not possible, until the task is at least many times easier than is necessary on the normal side. Thus, all our measurements are comparative, and each case yields its own standard. Otherwise such tests as the compasses, recognition of relative weight and size, and all attempts to estimate painful stimuli, are useless and fallacious for observations on the sick.

Sometimes, especially with lesions of the spinal cord, the opposite extremity to that mainly affected was also in a condition of abnormal sensibility, and it was impossible to obtain a standard for comparison from equivalent parts of the body. Under these circumstances we were obliged to compare the abnormal records with those from the hand or arm; such results must, however, be used with caution. No attention should be paid to the small variations in accuracy of response, and we have considered large differences only.

A. — SPONTANEOUS SENSATIONS

The examination was begun by obtaining from the patient a description of any abnormal sensations he may experience in the affected parts, such as pain, numbness or tingling. As these terms may imply in ordinary phraseology very different conditions, it is necessary to determine as exactly as possible in what sense they are used by the patient. " Numbness " may signify a " loss of feeling," or it may be used to describe, not a loss of function, but a positive abnormal sensation. Sometimes it may even signify inability to make delicate movements, especially in the fingers.

When spontaneous sensations exist, it is important to ascertain the con- ditions under which they occur, whether they are constant, and if they are aggravated by any external agent, such as contact, heat or cold.

We are accustomed to inquire if the patient has noticed at any time that he is unaware of the position in which the affected limbs lie, and if he

METHODS OF EXAMINING SENSATION 15

preserves an idea or mental picture of the limb. Many patients with cerebral lesions complain that when they wake at night they do not know where the arm is lying, and it sometimes seems as if part of the limb, such as the hand, had disappeared.

In cases of injury to the spinal cord the patient not uncommonly has an idea that his legs are in some definite position, although he is entirety insensitive below the waist. This illusory posture may not be constant, but may come and go, or change its direction at different periods in the course of the illness.

B. — Loss or SENSATION 1. Touch.

(a) Light touch is always examined first by applying a \visp of fine cotton wool gently to the skin, so that it does not produce gross pressure or deformation of structure. But this test must be used with extreme caution. Many brands of cotton wool, when rolled into a wisp, form so stiff a mass that sensations of pressure are evoked ; or, on the contrary, the finer quality of cotton wool may fail to act as a stimulus to the horny palm of a workman, or even to some parts of a normal well-kept hand.

Over hair-clad parts cotton wool is not a specific stimulus, but excites both protopathic and epicritic sensibility. After complete division and suture of a peripheral nerve, the affected area, if covered with hair, not uncommonly regains its sensibility to contacts with cotton wool in a few weeks. But when the hairs are removed by shaving, the skin is found to be insensitive, and may remain so for many months. This double tactile innervation of the skin of hair-clad parts is particularly liable to lead to fallacious conclusions in cases such as injury to the ulnar nerve ; it may seem as if sensibility to light touch had returned to the dorsal aspect of the hand, and yet after careful shaving this area is found to be entirely insensitive to cotton wool. This factor also played a great part in the sensations I experienced during the recovery of my arm, which are fully described on p. 272.

In cases of thalamic over -reaction cotton wool produces over hair-clad parts a peculiar sensation which has nothing to do with the sensory activities of the cortex. It is an affective response, which may take the form, on the one hand, of pleasurable " tickling," or, on the other, of uncomfortable " itching."

We have measured the sensibility to light touch by means of von Frey's graduated hairs ; these depend on the fact that a constant pressure is exerted by the tip of a hair when sufficient force is used to bend it. We can arrive at the amount of this pressure per unit area if the force exerted in bending the hair, measured on a balance, is divided by its total area in mm.2; the result expressed in grm./mm.2 represents the pressure per unit area.

But von Frey contends ([36] pp. 223-9), and we believe rightly, that this is not a correct method of comparing the value of different hairs as a

16 STUDIES IN NEUROLOGY

measure of light touch. For this purpose he divides the pressure in milli- grammes by the radius of a circle of the same area as the elliptical cross- section of the hair. The result expressed in grm./mm. represents the tension of the hair.1

Throughout the observations on my arm we were careful to bear this difference in mind, not only in the pressure exerted per unit area given in grm./mm.2, but the hair is also spoken of as "No. 3," "No. 6," etc., which expresses the tension in grm./mm. For clinical purposes these refinements are unnecessary, and, whenever the tactile hairs are employed in pathological cases, the measurements are recorded in grm./mm.2, the pressure per unit area.

In the following table we give the necessary data for determining the force exerted by the battery of test hairs we have used in our researches. But it is unnecessary for the clinical observer to provide himself with many hairs ; those exercising a pressure of about 14, 21, 23, 35, 70 and 100 grm./mm.2 are sufficient for practical work. Of these the first is useful for testing tactile sensibility on such parts as the palmar aspect of the fingers. Hairless parts, such as the palm and sole of the foot, which respond to cotton wool, will usually be found to be sensitive to a hair of 21 grm./mm.2. If cutaneous sensibility is completely absent, but the deep parts remain highly sensitive, they may respond to a hair of from 23 to 35 grm./mm.2, which is well above the threshold for light touch over normal areas.2

A lesion of the cerebral cortex may produce a peculiar uncertainty in the response to measured tactile stimuli ; the patient may be able to appreciate the contact of a certain hair at one time, but not at another. This is not confined to a small range of difference in the pressure exerted per unit area, as is the case with normal sensibility ; but the uncertain responses may be equally evident with 21 and 100 grm./mm.2. In such cases sixteen contacts with the same hair were made in one minute ; this rate allowed us to vary the intervals between any two touches, so as to avoid the tendency to rhythmical replies, so common over areas of defective sensibility. On the affected side, the first hair selected is one which can be easily appreciated over similar normal parts ; then hair after hair of increasing strength is applied, at a rate

1 Thus on the following table the hairs which have a tension of 4 grm./mm. and 5 grm./mm. both happen to exercise a pressure per unit area of 21 grm./mm.2 ; and yet, from the point of view of tactile sensibility, 5 grm./mm. is undoubtedly a stronger stimulus.

2 The actual hairs we have used were made for us by Professor von .Frey. They are kept in a metal box with the handles supported on a rack, so that the hair remains entirely free from contact when at rest. The force required to bend them vanes according to use and to the condition of the atmosphere ; but, at the end of six years' continuous work, 14 grm./mm.2 turned the scale at 0'21 grm., 21 grm./mm.2 at 0'32 grm. and 23 grm./mm.2 at a little over 0-8 grm. We wish to protest against a common variation of von Frey's apparatus, which consists of a single hair in a metal sheath, so arranged that it can be protruded or withdrawn to a varying extent. The condition of such a hair changes greatly, and the pressure necessary to bend it varies from time to time, even when it is extruded from its sheath to the same amount. Moreover, in order that the hair may not suffer by the extension and withdrawal, it must of necessity be thicker and coarser than when the test is made with a set of hairs, each permanently affixed to its own handle.

METHODS OF EXAMINING SENSATION

17

of sixteen times in the minute, until either the maximum threshold is passed or the strongest purely tactile hair is reached. Frequently we then go back- wards to the hair with which the testing began. No word is spoken throughout such a series of tests, which always end with a final set of contacts on the normal parts. This is necessary in order to be certain that the patient's general powers of attention have not deteriorated during the course of the examination.

Each correct answer is recorded by a vertical stroke and failure to reply by an 0; hallucinatory responses, if they occur, are marked by a broken stroke. From such a record the proportion of correct answers, and the order in which they occurred, can be studied at leisure ; thus the condition of tactile sensibility is not a matter of unsupported personal opinion.

Pressure in grammes.	Measured radii > in /it.	Total area in mm.2	Radius of a circle of the same area in /t.	Pressure per unit area.	Tension.
0-4	30 X 54	0-005	40 8 grm./mm.2	1 grm./mm.
o-i	47-5 X 57-5	0-0085	52	12 grm./mm.2	2 grm./mm.
0-21	55 X 90	0-015	70	14 grm./mm.2	3 grm./mm.
0-23	40 X 80	0-011	58	21 grm./mm.2	4 grm./mm.
0-30	60 x 90	0-017	73-5	21 grm./mm.2	5 grm./mm.
0-88	100 X 120	0-0377	110	23 grm./mm.2	8 grm./mm.
1-4	100 x 130	0-041	114	35 grm./mm.2	12 grm./mm.
1-8	115 X 125	0-045	120	40 grm./mm.2	15 grm./mm.
3	115 X 115	0-042	115	70 grm./mm.2	26 grm./mm.
3-6	100 x 130	0-041	114	90 grm./mm.2	32 grm./mm.
3-5	80 X 140	0-035	110	100 grm./mm.2	32 grm./mm.

Hairs exciting a pressure of more than 100 grm./mm.2 usually cause a sensation of pricking, and we have therefore avoided their use in all observa- tions on tactile sensibility. But those ranging from 70 grm./mm.2 up to 260 grm./mm.2 are sometimes useful as a measure of cutaneous painful sensibility.

A camel's -hair brush is not a satisfactory method of testing light touch. For, in the case of my hand, we were able to show that whether a sensation was or was not elicited by such a stimulus, when the skin was entirely insensitive, depended on the way in which the brush was used. If applied suddenly and vertically to the skin, so as to cause a jarring contact, a slight sensation of touch was produced; but when the pressure was made more gradually no sensation was evoked until distinct deformation of the brush occurred; even with these precautions it required slight pressure only to cause a sensation. Thus a camel's -hair brush stimulates both the cutaneous and deep sense organs, and cannot be considered as a test for superficial or light touch.

(6) Pressure touch can be roughly tested by means of some blunt object, such as the unsharpened end of a pencil or the pulp of the observer's finger, so long as its surface temperature does not differ widely from that of the part to be examined.

VOL. I. C

©©,-

18

For the determination of the threshold for pressure-touch we have employed a simple form of pressure-sesthesiometer (fig. 1). This consists of a vulcanite cylinder (A), pierced in its length to allow a thin steel rod (B) to move freely in it. Each end of this rod projects some distance beyond the ends of the cylinder; one end is pointed and shod with a cork or vulcanite disc 3 mm. in diameter (F), which we have adopted as a standard area, while near the other end there is a small platform. (C) on which weights, pierced in their centre, may rest. The weight of the steel rod with the contact disc is 2 grm., and this is consequently the pressure which falls on the skin when the unloaded instrument is brought vertically in contact with it ; but by adding weights this pressure can be increased up to 50 grm. or more if necessary. The instrument is held by the vulcanite cylinder and the cork disc is brought gently in contact with the part to be tested; then by depressing the cylinder the desired weight falls on the surface. The instru- ment is simple, and suffers only from the disadvantage that it must be used vertically. The minimal pressure that can be applied by it is necessarily high, owing to the weight of the steel rod, and is about 2 grm. This pressure on a 3 mm. disc can be always and constantly appreciated on normal parts, and the instrument is consequently of use only after @F tests with von Frey's hair or cotton wool have shown that there is an alteration of tactile sensibility.

In attempting to determine a threshold with this aesthesio- nieter we adopt the procedure described for von Frey's hairs, beginning with a low pressure and increasing after each series of contacts until a weight is reached with which the sixteen successive contacts in one minute can be appreciated.

2. Pain.

(a) Superficial pain. — Sensibility to pain may be tested first by pricking with a sharp steel pin or needle ; the reaction to the prick should be observed, and the patient asked to compare the sensations he experiences when normal and affected parts are pricked in close succession. It must be remembered that even in this simple test there is a danger of confusion, as the contact of a point, in addition to evoking pain, gives an idea of " sharpness " due to the appreciation of the relative smallness of the stimulating object. Consequently, if the power of recognising relative size is disturbed, the prick of a pin may be described as " less sharp " on the abnormal parts, although the pain evoked may be as great, or even greater, than on the normal side. It is therefore necessary to ensure that the patient distinguishes between the sharpness of the stimulus and the pain of soreness it produces. Unhappily,

FIG. 1. The Pressure-

METHODS OF EXAMINING SENSATION 19

this is often difficult, and care must be taken to guard against this source of error before deciding that sensibility to pain is disturbed solely on the ground that pricks are described as " less sharp " than over normal parts.

If the loss is slight, it becomes necessary to determine the threshold for pain. We have consequently employed, as a rule, a simple form of spring algesimeter (fig. 2). It consists of a metal tube (A) about 15 cm. in length, closed at one end and containing at the other a piece of vulcanite (B), flattened at its projecting end and perforated to allow the projection of a needle (C). The tube contains a fine steel rod, to one end of which this needle is attached. A fine spiral spring is fixed to the blunt end of this rod, and the other end of the spring is inserted into a small bar (F) which projects into the tube through a slit (a ... 6) in one D~ side of it, and is carried on a collar (E) that runs on the outer side of the tube. The spring is so arranged that it exerts no traction on the needle when the collar is at the highest point of the slit, and if the instrument is then applied vertically the point of the needle bears its own weight only. If, however, the collar is slid down towards the point of the needle tension is put on the spring and exerts a corresponding pressure on the needle. By measuring this on a balance the instrument can be graduated according to the pressure in grammes exerted on the needle, when the collar stands at different points of the scale. An instrument graded between 2 grm. and 10 grm. is E 2 sufficient for ordinary clinical purposes. When it is used F''' horizontally, or with the point upwards, these values vary according to the weight of the needle, but this variation can be easily calculated. When, however, as in our work, it is sought to obtain a relative or comparative rather than an absolute threshold , this is unessential, provided the instrument be applied c " " at the same angle to the corresponding points of the two sides of the body.

It has always been recognised that it is difficult to obtain an accurate threshold for painful prick ; for if a pin be applied with the same moderate pressure twice in succession to the same part, one contact may be appreciated as pain and the other as touch, depending largely on whether a pain-spot is directly stimulated or not. We consequently apply the algesimeter a certain number of times in close succession to the part to be examined, asking the patient to say whether he appreciates a prick or merely a touch, and take the reply for this series of stimulations instead of for each individual one.

We have found the interrupted current an unsatisfactory means of measuring sensibility to pain, and have not used it systematically in those researches.

(6) Pressure pain. — Whenever pressure is appreciated after division of a

20 STUDIES IN NEUROLOGY

peripheral nerve to the skin, its steady increase leads to the production of pain. But when the lesion is situated within the spinal cord, this is not the case, and it is therefore necessary to have some means of measuring the amount of pressure capable of causing pain. For this purpose we have used a modification of Cattell's algometer suggested by Dr. Rivers. The end of

the instrument is placed on the part to be tested, and pressure is exerted on the round knob which fits into the palm of the observer's hand. This compresses a spring in the handle. On the rod slides a scale, which is pushed down as the shaft is driven upwards by the increasing pressure (fig. 3).

Immediately the patient calls out that the pressure has become painful, the instrument is removed, the rod springs out of the handle again, carrying with it the scale, which remains at the point where the rod emerged from the handle at the moment of maximum pres- sure reached during that observa- tion. A line drawn round the rod acts as an indicator, and the amount of pressure applied can be read off at leisure from the relation of this line to the measure on the scale, which is graduated in kilo- grams.

We have found an algometer , constructed on these principles

A. — knows the algometer before use. Ine zero ot T/V

the scale corresponds to the horizontal line on the rod. Satisfactory. It Will give different

B.— Shows the algometer after use. The horizontal rparjjT10.sl ;n +},„ hands of parh

line on the rod now corresponds to 10 divisions on readings

the scale. At this point the patient complained that observer according to Variations

the pressure caused pain. The graduations correspond . , ,

to kilograms. in the manner and rapidity with

which it is applied. But although

the actual amount of pressure necessary to cause pain varies according to this personal equation, a comparison of the records on the normal and abnormal sides in the same patient shows a remarkable similarity with different skilled observers.

At least three or more readings must be taken over every part examined, as the answers vary considerably according to the state of expectation in the patient's mind.

FIG. 3.

METHODS OF EXAMINING SENSATION 21

3. Temperature.

Many difficulties surround the testing of sensibility to heat and cold, particularly as minor degrees of temperature play so considerable a part in our investigations. The use of ordinary glass test-tubes is open to serious objection except for the coarsest observations, for the wall of the tube is never at the same temperature as the fluid it contains. Thus, a thermometer placed in the water does not register even approximately the actual tem- perature applied to the patient's skin. We have therefore used flat-bottomed silver tubes with a diameter of T25 cm. These tubes were filled with broken ice, or with water at the temperature desired, and contained a thermometer. They were never warmed or cooled from without. When used for testing sensibility to heat, several tubes ranged in a wooden stand were filled with water at temperatures considerably higher than those we wished to use for testing ; from these, a tube was selected as soon as it had sunk to the temperature required. These silver tubes lose their heat so rapidly that it is impossible to use the same one for more than a short series of tests.

Sometimes, when testing large areas of sensibility to heat or to cold produced by lesions of the spinal cord, we have employed large copper tubes of 4 cm. in diameter. These retain their temperature much longer than the smaller silver tubes, and are particularly useful when we are concerned mainly with the existence of sensibility either to heat or to cold rather than with the exact degree of thermal stimulation; they also form an excellent means of evoking a thalamic over-reaction to temperature stimuli.

It is well to remember, when testing the scalp, that the hair insulates the skin, so that both heat and cold pass through with difficulty, and the results are liable to be unsatisfactory.

Few difficulties attend the testing of sensibility to the more extreme degrees of heat and cold. But occasionally, when the affected parts are sensitive to painful stimuli but not to heat, a tube of 50° C. or above may be said to be hot solely on account of the peculiar pain produced. This is particularly the case when sensation is returning after division of a peripheral nerve, or with lesions of the spinal cord which destroy sensibility to heat but not to painful stimuli. During the experiments on my arm, when tested with these temperatures, I frequently said, " Any ordinary patient would have called such stimuli hot, because the pain produced is of a kind associated in daily life with the action of hot bodies only. Further, a patient is told to say if he feels heat, cold, or a touch. Given, then, that he knows his thermal sensibility is being tested, he would certainly call the sensation I experience ' hot.' '

Occasionally contact with a neutral tube would cause an indeterminate and somewhat tingling sensation over the affected area ; this was frequently

22 STUDIES IN NEUROLOGY

said to be warm, and was one of the greatest difficulties against which we had to contend (vide p. 286).

A most disturbing condition, familiar to all who have investigated cases of lesions of the spinal cord, is the tendency of the patient to call all tem- perature stimuli, whether hot or cold, by the same name. It is important, under such circumstances, to interject frequent stimulations with a tube that is neither hot nor cold to the normal skin. Then it may be discovered that the neutral tube is as frequently said to be hot or cold as one which is a positive thermal stimulus to the normal hand.

Cerebral lesions do not as a rule abolish sensation to heat or to cold ; ice and water at 45° C. are usually appreciated without difficulty. But such temperatures form a ready method of applying measurable affective stimuli, especially in cases of the so-called " thalamic syndrome." Extremes of heat and cold are uncomfortable or even painful, whilst warmth is usually distinctly pleasant. To study this affective aspect of sensation it is generally advisable to apply the stimulus to a larger area, and for this purpose we have used large copper tubes with a diameter of 4 cm. filled with water at various temperatures.

In cases of cortical injury or disease it is important to determine the power of distinguishing the relative warmth of two tubes, each of which is recognised as warm. One of the most interesting defects in such cases is the inability to appreciate with any certainty the difference between 35° C. and 45° C. ; and yet both are said to be warm. Sometimes the loss of dis- crimination is less severe, but the patient cannot appreciate the difference between 33° C. and 40° C.

Occasionally it is important to determine the threshold for heat and for cold on similar portions of the two halves of the body ; this gives the range of the neutral zone, which may be considerably enlarged as the result of a cortical lesion. This is frequently an extremely difficult and unsatisfactory form of examination, for most patients possess no word which expresses a neutral sensation. Before we begin testing with this purpose we therefore suggest that the answer shall be " warm touch," " cold touch," or " nothing but a touch." At the same time we compare the sensation evoked by the neutral temperature with that of a distinctly warm or cold tube.

During the experiments on my hand we were much occupied with the site and mode of reaction of the heat- and cold-spots. They are of purely scientific interest, and can rarely be tested under clinical conditions. The cold-spots were sought for with copper rods of about 1 mm. in diameter, which were placed in a glass containing broken ice; on removal, each rod was carefully wiped and, after its flat base had once been applied to the skin, was returned to the ice.

For the discovery of heat-spots we used a simple method which, as far as we can discover, has not been described before. We chose a " soldering iron " consisting of a large copper block fixed to an iron rod let into a wooden

METHODS OF EXAMINING SENSATION 23

handle. This block, about 3 in. (7-5 cm.) in length and 1 in. (2-5 cm.) across every face, we cut down to a pyramidal point. The apex of the pyramid was flat and 1 mm. square. Into the copper block we bored a circular shaft passing obliquely downwards in the direction of the point. This was of sufficient size to contain the bulb of a thermometer, just under 1 cm. in diameter.

Two of these irons were placed in a jug containing hot water. When sufficiently heated, one cf them was removed and dried; the thermometer was placed in the cavity and the instrument laid on a cloth until the required temperature was recorded. It was then held firmly in the hand like a large pen, and lightly applied, vertically, to the surface of the skin. So large a block of copper retains its heat for a considerable time, and the thermometer gives a sufficient indication of its temperature. This should lie between 50° C. and 40° C., preferably at about 45° C. Higher temperatures cause distinct pain, which complicates the observations ; a temperature below 40° C. fails to stimulate most of the heat-spots.

A low external temperature greatly increased the difficulty in discovering both heat- and cold-spots ; and in the winter, when the affected hand seemed numb and cold, previous immersion in warm water greatly facilitated their determination.

4. Roughness.

The threshold for the appreciation of roughness is most conveniently determined by the Graham-Brown sesthesiometer. This consists of a mass of brass with a polished surface, from which a tooth may be projected by means of a graduated screw. The instrument is drawn firmly over the part to be tested, and after each application the tooth is projected further until the patient can recognise the roughness. When the threshold is normal this is generally apparent to the observer's fingers holding the instrument at the same time as to the patient. The tooth " rakes " the skin, and this stimulus is conveyed both to the observer and the sense organs of the patient, pro- vided his sensation is normal. Throughout this work we have used the original form of the instrument with one projection rather than that with many projecting cylinders.

We have used for the same purpose emery- or glass-paper of different degrees of roughness. We have adopted five grades, and employ as a control a piece of smooth cardboard of the same thickness. The normal ringers, when drawn over the rough surface, can recognise even the finest emery- paper we employ as rough, and can easily distinguish the relative roughness of any two grades. When this form of sensation is affected the finest grade that can be recognised as rough represents the amount of the defect. This is a useful test in cases of cerebral lesions, for by it the power of discriminating the relative roughness of two grades tested in succession may easily be determined.

24 STUDIES IN NEUROLOGY

5. Tickling and Scraping.

Our investigations led us to seek stimuli which are largely affective, or which contain a considerable affective component. Apart from pain, it is difficult to obtain a stimulus of this kind, but tickling unquestionably evokes a sensation which is strongly affective and may be either pleasant or unpleasant. The easiest method to produce tickling is to draw the pulps of the fingers gently over the soles of the feet ; in some cases this stimulus also tickles the palms of the hands. In certain persons a wisp of cotton wool rubbed gently over hair-clad parts produces tickling, especially over the pinna, on the neck and on the hair behind the ears, although in many such a stimulus is entirely ineffective for this purpose.

Scraping with the finger-nails is also a definite affective stimulus of the unpleasant order, as may be seen in cases in which there is an exaggerated response to affective stimuli. In such " thalamic " patients it may produce an intensely unpleasant sensation.

6. Vibration.

To test the power of recognising vibration we have employed a large tuning-fork beating 128 vibrations per second (C°).

The fork, vibrating strongly, is placed on some part of the body which is firmly supported on the bed or on a pillow. If it is normal, the patient at once recognises the " buzzing " sensation. His eyes are closed and he is asked to say when the vibration ceases ; !as soon as he indicates that it is no longer perceived, the fork is transferred to the corresponding portion of the other hand. Under normal conditions the vibration usually becomes appreciable again for a time. The period between the transference of the fork to the other hand and the moment when its beating can no longer be recognised, is measured with a stop-watch. In healthy individuals this may last from five up to fifteen seconds ; but a few persons allow the fork to run down so far on its first application that it has ceased to beat before it is transferred. Both these modes of reaction are normal, provided the measured periods are approxi- mately equal from right to left and from left to right. Thus it may happen that, in one form of normal response, the records read as follows for four observations :—

Right to left. + 6 sec. + 4 sec.

Left to right. + 5 sec. + 4 sec.

or, according to the other mode of reaction : —

Sight to left. + 0 sec. + 0 sec.

Left to right. + 0 sec. + 0 sec.

In neither instance was there any material difference between the two

hands.

METHODS OF EXAMINING SENSATION 25

A characteristic abnormal response is the following, taken from a case of injury to the cortex : —

Thumb : — •

Bight to left. + 8 sec. + 9 sec.

Left to right. + 8 sec. + 7 sec.

Middle Finger : — -

Sight to left. + 10 sec. + 10 sec.

Left to right. + 6 sec. + 6 sec.

Little Finger: — •

Sight to left. +15 sec. + 10 sec.

Left to right + 0 sec. + 0 sec.

Here the readings from the right thumb were normal, those from the middle finger slightly, and those from the little finger grossly, affected.

7. Localisation.

Various methods have been described to test the faculty of localisation of tactile and other stimuli on the surface of the body. We have experimented with most of them, but have found a modification of Henri's method the most suitable for clinical purposes.

In Henri's original method the patient was required to mark on a life-sized diagram or photograph the exact situation of the spot stimulated, while the observer indicated on a duplicate diagram the spot he touched. Simple though this method is, it labours under the disadvantage that many patients find a difficulty in translating an image of the part tested on to a diagram which can show only two planes of space.1 We found that this difficulty disappeared when the diagram was replaced by the corresponding part of another individual. The part to be tested, for instance the left hand, is hidden from the patient by a screen, while the left hand of one of the observers is presented to him, placed in a similar position to that of his own limb. On this living model of his hand the patient indicates with his other forefinger the exact spot on which he believes he has been touched. The second observer marks on a diagram the spot that is touched, together with the spot indicated by the patient, and thus a permanent record is obtained. In order to point to the spot that has been stimulated, when one hand is seriously paralysed,

1 This was by no means the case in myself, and in the experiment on my hand we relied greatly on this method. With my strong powers of visualisation I rapidly developed what may be called a visual map of the affected area. I had but to close my eyes to see a picture of my hand with the affected area marked upon it as clearly as in a photograph. As soon as a spot was stimulated, I saw its position on this map and at once described the neighbouring landmarks. I could even give approx mate measurements; for instance, I would say that the . point stimulated lay in " the interosseous space about 1 in. from the head of the first meta- carpal." Occasionally I was allowed to point with the index-finger of the right hand; but, since this in itself acts as a stimulus, it should be rarely permitted and should be reserved for special occasions.

26 STUDIES IN NEUROLOGY

the patient must usually withdraw the normal hand from behind the screen when control observations are being made upon it.

When the loss of sensibility affects the foot, we employ an exactly analogous method, and the errors of localisation are recorded on diagrams of the foot. The living model, upon which the patient localises the spot touched in himself, consists either of the foot of one of the observers, or, more often, of the corresponding lower extremity of some other patient.

Occasionally we have also used the method in which the patient names the spot stimulated. But accurate results cannot be obtained by this method, and it labours under the serious disadvantage that confusion frequently arises in the terms employed to designate the different parts, such as the fingers or their segments.1

The groping method is useless as a means of testing the power of localisation, as the results obtained by it are gravely affected by any coincident disturbance of the power of recognising the position in space of the part tested.

8. The Compass Test.

(a) Simultaneous Application of Two Points. — To test the power of dis- criminating two points we have usually employed a pair of carpenter's com- passes, the points of which had been ground down until they gave no sensation of sharpness. Most of the instruments, called " sesthesiometers," used for this purpose are provided with points so sharp as to be wholly useless.

These large compasses are excellent for observations made in a hospital, but they are clumsy for the daily run of clinical work. A modification, which has been devised by Dr. Gordon Holmes, consists of two flat triangular pieces of steel 10 cm. in length and 1-25 cm. in breadth across the base. Each limb ends in a rounded point which has been twisted out of the horizontal so that it makes an angle of roughly 45° with the axis of the steel bar. The two limbs are hinged together at their broad bases so as to form a small pair of compasses that can be carried in the waistcoat pocket. On the flat surface of each bar, which becomes more and more exposed when the limbs of the compasses are separated from one another, lines are engraved corresponding to the distance separating the points ; thus, when they are 1 cm. apart, the edge of the flat bar corresponds to one of these lines, 2 cm. to another, and so on, up to a distance of 10 cm.

For recording our observations we used the method suggested by McDougall (72). The compass points were set at a certain distance from one another; they were then applied to the part to be tested in such a way that sometimes two points, sometimes one point only, touched the skin. The stimuli followed one another in an entirely irregular order, but so that, ultimately, the patient

1 For example, the index is sometimes said to be the "first," sometimes the "second finger"; the little finger may be called the "fourth" or "fifth finger." The "first joint" of a digit may be either the proximal or distal phalanx.

METHODS OF EXAMINING SENSATION 27

had been touched ten times with one point, ten times with two points. Each correct answer was marked with a stroke, whereas a mistake was recorded by a cross. Thus, if he answered " one " when touched with two points, a cross was placed below the line ; if one point had been called " two," the cross was marked above. By this method it was at once obvious in how many instances he had answered correctly among the ten single and ten double stimuli. The answers, whether right or wrong, were ranged in strict sequence above and beloAV the horizontal line.

Perfect appreciation of the compass points at a distance of 4 cm. would be represented thus : —

l I III II mi I

4 cm. ~

mi in in

If, however, the patient was unable to differentiate the two points, answering " one " to every stimulation, the record would stand : —

4cm 1 1 nn _ n _ mi

2 I XX XXX X XXXX

Less complete failure would be represented by some such formula as :—

jj _ IIXX _ XI _ IXXI m* 2 I XIX IIXX XXI

In the following pages these records are sometimes translated into the number of answers which were right (B.) or wrong (W.), for the sake of simplicity.

Throughout our researches, unless expressly stated, all compass tests have been applied in the longitudinal axis of the limb.

The results obtained with this test are profoundly influenced by accessory conditions. A stranger entering the room, or anything that disturbs the patient's state of quiet attention, profoundly diminishes the accuracy of his answers. Thus in my own case on one occasion R.'s servant entered our workroom in the middle of an almost perfect series of answers : they at once became less accurate : —

6cm 1|2R' 3W' m< 2 | o R. 5 W.

After his withdrawal I again began to answer as before : —

6cm 1|9R"

l'

2 | 9 R. 1 W.

Any profound cooling of the skin, or even the occurrence of a pilo-motor reflex, greatly diminishes the accuracy of the answers to compass stimulation. When the coat is removed, and the sleeve is rolled up, " goose-sldn " is fre- quently produced ; testing should not be begun until this has entirely passed away.

The compass points are set at a distance from one another which is just

28 STUDIES IN NEUROLOGY

above the threshold on the normal side, that is to say, at such a distance that the patient has no difficulty in recognising the two contacts when the points are applied simultaneously. Then the similar part on the affected half of the body is tested in the same way, with the compass points set at the same distance from one another. If this is found to be below the threshold, the points are separated until a threshold can be obtained, or, if this is not possible, a record is taken with the compasses separated to a distance many times greater than that at which a perfect reading was obtained on the normal side.

Such was our general procedure in clinical examinations. But in the case of my arm we were able to make more exhaustive observations, and always began a series of tests with the compass points widely separated from one another (9 cm.). Not uncommonly the records considerably improved as the distance was gradually diminished, and were frequently better at 7 cm. than at 9 cm.

This well-known phenomenon seemed, in my case, to be associated with the increasing detachment of attention from the procedure of testing. The following series of records obtained from the abnormal area on the left forearm are a good instance of such improvement : —

6 cm *' 5R- 5W- 5 cm 1'BB' 5 W' 4 cm l ' 9R" IW'

*' 2 | 10 R. *' 2 I 6 R. 4 W. m' 2j9 R. 1 W.

The improvement at 4 cm. was associated with complete wandering of attention from the manipulations. When at the close K. asked whether there was anything to say about these observations, I could have believed that nothing had been done. I was thinking about a book I had been reading, and was completely absorbed, until recalled by R.'s question.

Occasionally, especially after exercise in the open" air, this condition of detachment would pass into sleep. We noticed that the answers seemed to improve up to the point at which I ceased to reply, and therefore made several observations on the effect of somnolence on the compass records. On October 26, 1907, I fell asleep at the close of the following record : —

4cm 11

2 7 R. 3 W.

an unusually good formula for the affected forearm. I was wakened, and after a short interval it was found that the same distance of 4 cm. was completely below the threshold; every double stimulation was said to be "one." I was allowed again to settle myself in the armchair, and R. continued to test me with the points of the compasses at the same distance. With the return of the somnolent state the records improved; the total sixty stimulations gave the formula :—

4cm M21R. 9W. Cm'2|26R. 4W7

METHODS OF EXAMINING SENSATION 29

but of these the first and second twenty obtained when I was more nearly asleep were better than the last series.

First Series. Second Series.

1|6B. 4W. 1J 7 R. 3 W.

2 I 9 R. 1 W. 2 | 10 R.

This sleepy condition, which is so favourable for results with compasses, is one that requires absolute freedom from all external appeal to responsible action. It is a condition which I have never succeeded in producing surrounded by the multifarious interruptions of home.

Conversely, concentration on the details of the compass test greatly diminished the accuracy of the answers. During a large number of examina- tions, directed towards elucidation of the phenomenon of " double ones," I was asked to state whether the two sensations seemed to be far apart and, if possible, to indicate the position of the two spots. This required much con- centration of attention on the details of testing and considerably raised the threshold.

(6) Successive Application of Two Points. — But in addition to testing the ability to discriminate two points applied strictly simultaneously, we have found it necessary, when dealing with sensory disturbances from cerebral lesions, to investigate the power of recognising two points applied to the skin in close succession. This can be carried out by bringing down first one point and, whilst it remains in contact with the surface, rapidly placing the second point upon the skin. Evidently, the interval of time between the successive applica- tions must be short if the two points are to be appreciated as a double contact, and not simply as two successive touches. The following record, obtained from the affected forearm in a case where the power of recognising the double nature of the compass points was lost, whether they were applied simul- taneously or successively, illustrates the method by which we record the results of this test : —

r i | mi mill

15 cm. \ 2 |~ xxxx xxxx xx

I 2 + | XXX XXXX XX X

Here the compass points were separated by a distance of 15 cm., and the contact of one point was recognised in every case correctly. But two points applied simultaneously (2) or successively (2 +) were never said to be anything but one.

If the power of localising the spot touched is unaffected, the patient will retain the faculty of recognising two points applied successively, even though he may be unable to discriminate them when brought in contact with the skin strictly at the same moment. A record from the finger, under such conditions, may read as follows : —

ri | 11 1111 nil 2 cm. ' 2^ "xxx xx x xx __xx

[ 2 + j 11 1111 111 1

30 STUDIES IN NEUROLOGY

9. Position,

The power of recognising the posture of any part of the body is tested by placing a segment of a limb in some position and asking the patient to indicate where it has been placed, either by description or by imitation with the sound limb. A second method is to ask him to touch with the normal hand some definite spot, such as the tip of the index-finger or of the great toe ; this is a convenient test for knowledge of the position of the limb as a whole, especially if the faculty of localisation is intact. The power to succeed in this test may be influenced by a defect of the sense of position at any joint of the limb.

As ability to recognise the posture of the limb may be aided by the memory of the passive movement by which its present position was reached, it is advis- able to obviate this factor as far as possible. This may be done by keeping the patient's attention diverted from the movement by conversation or questions, and by allowing the limb to remain in the position to be tested for a short time before his attention is directed to it.

A measurement of a defect in the sense of position may be obtained by the method introduced by Horsley (56), but for this purpose it is necessary that the opposite limb should be normal. Horsley employed a glass plate graduated into half -centimetre squares, which could be placed, screened from the patient's sight, in any of the three planes of space. Instead of this glass plate, we have used a sheet of stiff cardboard, on one side of which a small depres- sion is made to receive the tip of the index-finger of the limb to be tested, while to the other side a sheet of white paper can be fastened. This card- board is placed in any position, and the patient is required to bring the normal index-finger towards the tip of its fellow, which lies on the opposite side ; the spot on which it impinges on the paper is marked by the observer. A series of ten successive observations is made in this way. The sheet of paper can be then removed from the cardboard plate, and forms a permanent record of the amount and direction of the error.

10. Passive Movement.

The power of recognising passive movement may be roughly tested by changing the position of a segment of the limb and asking the patient to indicate when he can appreciate the movement ; we then measure the extent through which the part must be moved in order that the direction of movement can be rightly perceived. It is always necessary to carry out control experiments on the opposite normal limb.

In order to measure the angle through which a movement must be made to be appreciated, we employ a simple instrument (fig. 4), which consists of a long narrow plate of brass (A), lined with cloth, that can be strapped on to any part of the limb by bands (B) attached to it, or held in contact with it by the observer. At one end of this plate an arm, which carries an arc of a

METHODS OF EXAMINING SENSATION

31

circle with degrees marked on it, is attached by a joint (D), movable in all directions. Two such arcs can be adapted to this instrument, either of which can be attached at (E) ; one (F) with a radius of 7-5 cm. for measuring move- ments of shorter segments, as those of the ringers, and another (G) with a radius of 15 cm. for longer segments. The brass plate is applied to the limb in such a way that the point (D) lies immediately over the joint at which the movement is to be measured, and the arc is then brought into the plane of the movement that is to be made. The range of movement necessary for appreciation can then be easily read off from the scale on the arc.

There are certain sources of error in obtaining such measurements. In the first place, the patient may reply, when he feels the pressure of the observer's fingers by which the passive movement is made ; but this can be easily obviated by grasping the part to be moved so firmly on two opposite surfaces that the additional pressure necessary to produce the movement cannot be distinguished. The part should be grasped between the fingers ap- plied to the surfaces that lie in the plane in which the movement is to be made, rather than

On the surfaces vertical The instrumenfc devised by Dr. Gordon Holmes to measure the to the plane of move- extent of the smallest appreciable passive movement. The finer

divisions of the scale are not shown upon this drawing for the sake ment ; ior in the latter Of clearness.

case the dragging and

displacement of the soft tissues may enable the patient to reply correctly,

though he cannot appreciate the actual movement.

In the second place, the rate of the passive movement may influence its appreciation. To obviate errors from this source we have attempted to make the movement roughly at a certain uniform rate, and, as our measurements have been always considered in relation to those obtained from the opposite sound limb, this safeguard is sufficient for clinical purposes.

Finally, in a normal limb a passive movement is appreciated, and its direction is recognised almost simultaneously; but, when sensibility to passive movement is affected by a cerebral lesion, a much larger range of movement may be required in order that the patient can obtain a knowledge of its direction, than that which enables him to recognise its

FIG. 4.

32 STUDIES IN NEUROLOGY

occurrence. It is therefore necessary in some cases to measure both separately.

11. Appreciation of Weight.

To test the appreciation of weight we have employed circular discs of lead 3 cm. in diameter, ranging from 20 grm. to 200 grm. in weight. The surface of each disc which is placed in contact with the body is covered with chamois leather, in order to prevent the coldness of the metal affecting the skin. This has the additional advantage that when the weights are placed one on the top of the other they have less tendency to slip.

With these weights we carry out the following series of tests, both with the hands fully supported and also when the patient is permitted to estimate the relative weight by " weighing," i. e., by raising and lowering his hands.

(a) With the Hand Supported. — Two weights are placed successively on the normal hand, and the patient is asked to say which is the heavier. With weights, of the surface area we use. even the least intelligent can recognise the difference between 70 and 100 grm., and many can give a series of right answers with 80 and 100 grm. Two weights are found which can be correctly distinguished on the normal hand, and they are then employed to test the affected hand in the same way. Usually in our cases, if the power of recog- nising weight was affected, the errors were gross, and in many instances no pair of weights could be found which could be distinguished with certainty. But, when the faculty of estimating relative weights was not completely lost, we were sometimes able to work out a true difference-threshold ; that is to say, two weights could be found bearing to one another such a relation that one was always said to be the heavier, while another pair, which differed to a less degree, could not be distinguished. At least four, and usually six or eight, observations are made with each pair of weights.

Next we test the power of recognising the increase" or decrease of weight. For this purpose a thin cork disc of the same diameter as the weights is first laid upon the palm. To this progressively heavier weights are added and then removed until the cork alone rests upon the palm. These weights are not added or removed in an unbroken sequence, but irregularly, and the patient is asked to indicate whenever any alteration in weight occurs. Thus the complete record of a series of observations might read as follows : —

Cork + 20 grm. + 40 grm. — 40 grm. + 40 grm. + 80 grm. — 80 grm. + 80 grm. + 100 grm. — 100 grm. — 80 grm. — 40 grm. — 20 grm.

First of all the sound hand is tested, and the patient's normal capacity determined; then a similar series of tests is applied to the affected hand. When the power of recognising addition or subtraction of weight is lost, the jarring produced by the manipulation may be appreciated ; this tactile sensa- tion, evoked by the act of removing one weight from, or adding it to another, is a fruitful source of error, but with care and practise can be reduced to a minimum. Moreover, by gently touching the weight without altering it, as

33

it lies on the hand, we can ascertain whether the patient's replies are due to recognition of a change in weight, or to the tactile stimulus evoked by the manipulations of addition or removal.

Finally, the patient is asked to compare two weights placed one on each fully supported hand.

(6) With the Hands Unsupported. — A weight is placed in each hand and the patient is asked to " weigh " them by raising and lowering his hands. Another method is to place a weight in one hand and then to substitute another one for it, each weight being raised and lowered several times. In normal persons the latter method gives the more accurate results, but our patients often became so confused on the affected hand by the absence of a normal standard that we have usually adopted the first form of this test.

12. Appreciation of Size.

The ability to recognise differences in size may be tested by placing in succession two objects of different size but of the same shape in contact with the part, and asking the patient to distinguish which is the larger. By varying the relative size of the objects, a threshold for this form of discrimination can be obtained. For this purpose we employ circular pieces of thick leather, increasing by half a centimetre, from 1 cm. to 4 cm. in diameter. Leather has the advantage that it is rarely cold to the skin, and pieces 4 to 5 mm. in thickness are sufficiently rigid for the purpose. Each disc is provided with a handle on one surface, by which it can be manipulated with ease.

The appreciation of size is most conveniently tested on the palms, as there the difference threshold is small.

The ability to distinguish the head from the point of a pin, when the latter is applied so gently that it does not prick, depends on the power of recognising relative size.

13. Appreciation of Shape in Two Dimensions.

By shape we mean the two-dimensional contour of an object that can be recognised on contact with the, surface of the body. To test this faculty we have employed simple shapes, generally a circle, a square, a triangle and an oblong, cut out of stiff leather. In the set we have found most convenient, each side of the square, the diameter of the circle, and the height of the triangle, were all 3-5 cm., while the oblong was also of this length and 1-75 cm. in breadth.

The shape of these objects can be easily distinguished on the normal palm when they are applied firmly and evenly, but unhappily they can rarely be recognised on most other parts of the body, including the soles of the feet.

14. Appreciation of Form in Three Dimensions.

We employ the word " form " to mean the three-dimensional shape of an object ; we test the ability to appreciate it by placing objects in the patient's hand, asking him to determine their form by feeling them and by moving them

VOL. I.

34

about between his fingers. Any common objects, such as a pencil, coin, knife, etc., may be employed for this test, but we have found it advisable to use, in addition, standard tests of geometrical form, such as a cube, a cylinder, an ovoid (called by the patients " an egg "), a cone and a pyramid, made in approximately the same bulk from wood. The patient is first asked to select his own names for them, or if description offers any difficulty he is allowed to point to the object he identifies in duplicates placed before him.

When there is serious paralysis of the fingers, the test-object must be moved about by the observer in the patient's hand; we have found this sufficient for appreciating the objects we use, when the ability to recognise form is not affected.

In addition to the power of appreciating these geometrical forms, we always test the patient's ability to recognise familiar objects, such as a knife, pencil or coin placed in his hand with the eyes closed.

15. Appreciation of Differences in Texture.

Interesting facts may be obtained by testing the patient's ability to recog- nise the texture of ordinary stuffs by touch. For this purpose we employ a set of common materials, calico, flannel, silk, cloth and ribbed velvet, which the patient is allowed to feel and move about between his fingers. Those we use can usually be identified with ease by the patient's normal hand.

With lesions of the cerebral cortex this test yields striking results, if carried out in the following manner. The patient is allowed to finger the various stuffs, first with the affected and then with the normal hand. After Ms answers have been recorded, an identical piece of the same texture, e. g. ribbed velvet, is placed in both hands at the same moment. He not infre- quently says " they are quite different " ; asked to explain this difference, an intelligent patient may give an interesting account of the diverse sensations evoked by stuffs of similar texture in the two hands.

CHAPTER III

CLINICAL APPLICATION OF THESE METHODS

SUCH were the methods we have employed to test sensation throughout our various researches ; some were found useful in one piece of work, some in another, but in the preceding chapter I have grouped them together according to the sensory categories to which they belong.

I have attempted to follow the impulses produced by an external stimulus from their origin on the periphery to their reception in the sensory centres, and it is obvious that some of these tests, which are of value with lesions of one part of the nervous system, are not applicable when the disturbance lies in some other portion. I shall therefore attempt shortly to indicate the methods which have been found most useful, when the sensory paths have been interrupted in various anatomical situations. At the same time I have appended a short general scheme of examination suitable to each of the main divisions of the nervous system.

(1) With Lesions of the Peripheral Nervous System. Name — Address — Age — Occupation —

Injury — Date — Cause — Nature —

Nerve or Nerves affected — (Radiographic examination if necessary.)

Motor Power —

Defects of movement —

Muscles which are paralysed or show some loss of power —

Normal muscles in the affected limb —

Wasting —

Electrical Reactions. (These tests should be deferred until the end of

the examination.)

35

36 STUDIES IN NEUROLOGY

Trophic changes (nails, hair, skin, etc.)— Vasamoivr changes and Sweating —

Sensation —

Pain or other Spontaneous Sensations —

" Tenderness," " Over-reaction," " Hyperalgesia "•

Form of stimulation by which it can be evoked—

Is it relieved by heat or cold?

Character of the pain or discomfort ; does it radiate widely ?

Distribution — Loss of sensation —

To Cotton Wool (or to tactile hairs if necessary)—

To Prick- To Pressure (observe if the sensation of pressure is accurately localised or not) —

To Painful Pressure —

To Heat and Cold—

(Recognition of Passive Movements if necessary as corroboratioii of loss of deep sensibility.)

Surgical Record —

First the patient is asked to give an account of any spontaneous sensa- tions which he experiences in his daily life as the result of nerve injury. If he suffers from pain, its distribution is recorded on a chart together with a short account of its character. It is important to note how these abnormal sensations behave both to changes in atmospheric conditions and on warming or cooling the affected parts.

Then the affected limb is examined for " hyperalgesia " and " tender- ness." These two conditions are not identical; for, as we have shown, a part of the body may react excessively to painful stimuli and yet be in a condition of lowered sensibility even to pain. No area can be called " hyperalgesic " in the strict sense of the word unless the measurable aspects of sensation have at least a normal threshold. This condition is rare except as the result of direct irritation of some nerve trunk.

On the other hand, over -reaction to potentially disagreeable stimuli is a common sequel to lesions of the peripheral nervous system. For example, after complete division of the median, the whole of the area assigned anatomically to this nerve is rarely, if ever, insensitive to the prick of a pin. Moreover, if a pin is dragged gently across the palm from the ulnar side the patient usually cries out as soon as it passes to the radial aspect of this anatomical border. He complains that it is " more sensitive " ; asked to explain his meaning he insists that " it hurts more " and that " the feeling runs into my fingers; it is like electricity." Otherwise he may say, "it is numb but it hurts." When a pin is dragged lightly in an opposite direction

CLINICAL APPLICATION OF THESE METHODS 37

from the radial towards the ulnar half of the hand, an intelligent patient recognises that sensation becomes " all right" as soon as it has passed the anatomical boundary assigned to the median nerve. But this observation requires more introspective ability on the part of the patient than recognition of a disagreeable change, when the pin travels in the opposite direction.

Many patients can mark out this border for themselves by passing the index finger of the normal hand across the palm and noting the points at which the sensation changes. This has nothing to do with a change in the texture of the skin, especially in the later stages of recovery of sensibility after nerve injury.

The same boundaries to the abnormal area can be defined with the help of hot and cold tubes, provided the temperature is above about 48° C. or below about 15° C. Such stimuli cause discomfort, and the patient usually withdraws his limb as soon as the over-reacting portions are reached.

This over-reaction to all forms of disagreeable stimulation gradually merges into parts completely insensitive to pricking ; this is the condition so commonly found in the hand some ten days or more after division of a peripheral nerve. But it is important to remember that in some parts of the body the border separating normal from abnormal is a well-defined line with no such over-reaction. This is the case whenever the boundaries of the loss to light touch and to prick are co-terminous, as, for example, with the anterior and internal border of the external popliteal.

When testing with cotton wool it is important to remember that contact with the hairs may evoke a response although the skin itself is insensitive. On the palm of the hand the boundaries of the loss to this form of tactile stimulus correspond to the " line of change," which can be worked out by dragging a pin lightly across from normal to abnormal parts. But on the back of the hand the presence of the hairs is a disturbing factor and the true boundaries of the loss of sensibility to cotton wool can only be determined after shaving. A similar rule applies to the upper limits of the external popliteal and to other branches supplying hair-clad areas of the body. Shaving, however, produces a material diminution of sensibility, and testing must not be carried out immediately after removing the hairs.

When cotton wool is employed with due precautions, the results are usually sufficient for diagnostic purposes. But it is not a measurable stimulus and the effects produced, even by the same wisp of cotton wool, differ according to the characters of the part to which it is applied and the idiosyncrasies of the observer. Over hairless parts, however, such as the palm of the hand and sole of the foot, the extent of the loss of sensibility usually corresponds to that revealed by a hair of 21 grm./mm2. (5 grm./mm.). But for all careful testing, or whenever there is the slightest ambiguity about the results obtained with cotton wool, they should be checked by means of von Frey's hairs.

Next we attempt to determine what parts are completely insensitive to the prick of a pin. The boundaries of this area are not, as a rule, well defined,

308410

38 STUDIES IN NEUROLOGY

but it merges gradually into portions where sensibility is present though grossly defective; this adds to the difficulty of recording the results on a chart. The limits of the analgesia differ from time to time and are peculiarly liable to vary with vascular changes or coldness of the limb.

Sometimes, when testing with a pin, the patient says that he appreciates the stimulus, although in reality he has no sensation of pricking, but recognises the pressure excited by the point. It is important to bear in mind this source of error; before recording the presence of sensibility to prick we must be certain that the patient is responding to its painful or uncomfortable aspect. Over areas of diminished sensation painful sensation is frequently spoken of as a " stinging or burning feeling."

With lesions of the peripheral nerves or posterior roots, an area sensitive to the tactile aspect of pressure also responds to the pain produced by raising it to an excessive amount. For example, after complete division of the median nerve at the wrist the terminal phalanges of the middle and index fingers may remain sensitive to firm contacts; if so, discomfort can be evoked by in- creasing the pressure. The fibres of the median nerve on which this deep sensibility depends are given off in the forearm and pass to the ringers by way of the long tendons. Presence or absence of sensations of pressure may be, therefore, of considerable diagnostic importance, especially if the wound is situated at the wrist ; for, if the tips of the index and middle fingers remain sensitive to pressure, these fibres have escaped and the tendons are probably intact, whilst if deep sensibility is absent they are likely to have been divided.

With peripheral nerve lesions it is usually unnecessary to measure the amount of pressure required to cause pain ; for if deep contacts can be appre- ciated, increasing the stimulus evokes discomfort, and considerable areas insensitive to prick may respond to the painful aspect of pressure. This is not the case when the lesion is situated in the spinal card, and such dissocia- tion of deep and superficial sensibility to pain may sometimes help to decide whether the injury is mainly in the posterior roots or cord.

Another function which depends on the presence of deep sensibility is the power of recognising posture and passive movements at the various joints. It is always well, especially with lesions affecting the upper extremity, to carry out these tests; but they are usually of corroborative rather than of primary diagnostic importance. Thus, with a complete lesion of the median nerve, the patient loses the power of appreciating movements at the terminal joints of the index and middle fingers ; but at the same time these phalanges become insensitive to the tactile or painful aspects of pressure.

The tuning fork is of little value as a test with lesions of the peripheral nerves, for the vibration spreads so widely across and along the limb that it is certain to reach some more or less normal portion unless many nerves or roots have been destroyed. This makes it all the more valuable as a means of discovering those changes in sensibility of hysterical origin which so frequently complicate the nerve injuries of war. Suppose a man has received

CLINICAL APPLICATION OF THESE METHODS 39

a gun-shot injury of the post-axial half of the forearm, he may present a complete loss of sensation over the post-axial portion of the palm and back of the hand together with total anaesthesia of the little finger and either the whole or a portion of the ring ringer. When the tuning fork is placed over the ulnar part of the hand, he does not appreciate its vibration until it has passed to the radial side of the anaesthetic border on the palm ; and yet the vibration can be easily recognised by the observer if he places his fingers over the thenar eminence of the affected hand. Had the patient suffered from a complete ulnar paralysis of organic origin, he would have himself appreciated the tuning fork everywhere except when it was placed over the distal phalanges of the little finger. The original defects of sensibility, aided by the suggestive testing methods of the surgeon, have evoked an hysterical anaesthesia, and the mind refuses to receive any impressions from a stimulus originating within this area, although it may produce widespread physical radiation.

Many difficulties surround the testing with heat and cold. We usually begin with two tubes filled with broken ice and with water at about 48° to 50° C., and with them we mark out the areas completely insensitive to thermal stimuli. But it is most important to remember that any temperature above about 45° C. may evoke pain and the " stinging " it causes is frequently called " hot " by the patient, although he may be unable to appreciate either heat or cold.

The limits of this complete insensibility to temperature stimuli rarely correspond to the full extent of the thermal loss, and it is usually necessary to carry out further observations with less extreme degrees. But tempera- tures round about 25° C. are frequently not appreciated in the winter, or the hand is cold and blue ; it is better, therefore, for diagnostic purposes to employ tubes containing water at 40° C. or below which can be recognised at once over the equivalent normal parts as producing a sensation of warmth. During recovery of sensibility after injury to a peripheral nerve the whole of the affected area may become sensitive to ice and water at 45° C., and yet temperatures of from 35° to 40° C. may evoke no response.

(2) With Lesions of the Spinal Cord, Bulb and Mid-brain. Name — Address — Age — Occupation —

Disease or Injury — Date of onset — Cause — Nature —

Situation of Injury — (Radiographic examination if necessary.)

40 STUDIES IN NEUROLOGY

Reflexes —

Wrist- jerks —

Triceps-jerks —

Superficial reflexes from palm —

Abdominal Reflexes —

Knee-jerks —

Ankle-jerks —

Ankle clonus —

Plantar reflexes (observe the action of the inner hamstrings) —

Cremaster reflex —

Bulbo-cavernosus reflex —

Perianal reflexes —

Involuntary Movements (" spontaneous " or evoked) — Character of movement — Flexor —

Up-going toe, flexion at ankle, knee, hip — Contraction of abdomen — Extensor —

Movements of the opposite limb (similar or opposed ; rhythmical)- Field from which the various involuntary movements can be evoked — Nature of the stimulus necessary to evoke these movements — Facilitation of visceral activity —

Motor Power —

Defects of movement —

Movements which can be carried out voluntarily —

Co-ordination (with eyes open and shut) —

Tone and Spasticity —

Wasting —

Power of standing (on one or both feet; with eyes open and shut) —

Gait—

Trophic Changes — Vaso-motor and Sweating —

Sensation —

Spontaneous (including Pains and Girdle sensations) — Areas of over-reaction — Loss to Touch — Loss to Pain —

Superficial —

Pressure —

Loss to Heat and Cold — Localisation —

CLINICAL APPLICATION OF THESE METHODS 41

Compass test —

Posture and Passive Movement — (If the hand is affected — weight —

size — form — texture.) Sphincters, etc. Bladder —

Voluntary or automatic. Retention — Measured physiological activity. Facilitation — Condition of sphincter — Sensation and desire —

Rectum —

Voluntary or automatic. Retention — Physiological activity. Facilitation — Condition of sphincter — Sensation and desire —

Genitalia —

Erection, emission, desire —

Sensory condition of penis, scrotum, testicles.

Surgical record —

Spontaneous root-pains are the most important sensations of which the patient may complain. They usually correspond to the level of the lesion and on the trunk extend more or less directly round the body from back to front. If the patient is asked to point to the situation of his pain, he usually places his hand on two spots, one behind and the other in front, which form the "maxima" for that particular area; sometimes in addition he selects another point on the lateral aspect of the trunk or he may draAV his hand right round his body at a certain level.

Not uncommonly such zones can be marked out by tenderness of the body wall. A pin is dragged gently from above downwards and then in the opposite direction across the parts indicated by the patient as the situation of his pain. The area which can be defined in this manner by " tenderness " of the superficial structures is not necessarily " hyperalgesic " ; for sensi- bility to pricking may be measurably less than normal although the reaction evoked is greater.

The form assumed by these areas corresponds more or less closely to the distribution of the fully developed eruption in herpes zoster; and the level of the affected roots can be determined by reference to the chart drawn up by Head and Campbell (45) from a series of post-mortem examinations in this disease. Diagrams based on analgesic borders are useless for this purpose. The significance of these root zones can be determined solely by the study of

42 STUDIES IN NEUROLOGY

residual sensibility (Sherririgton [108 and 109]), or of some irritative condition of radicular distribution such as the eruption of herpes zoster.

With serious injuries of the spinal cord, especially those associated with gross loss of sensation, the patient should be asked if he recognises the existence of the parts below the injury. Sometimes he " feels as if he had lost his legs " ; "it seemed as if my legs had been blown away." Otherwise he may recognise that his limbs are present, but thinks they are in some particular position, although he is entirely unable to appreciate their true posture at any moment. One of the earliest indications that the stage of shock is passing away is given by the appearance of " phantom " legs.

It is also important to inquire into the condition of visceral sensations. Can the patient appreciate that his stomach is full after a meal? Does he experience desire to micturate or to pass a motion? Can he tell when these acts occur ? Is he able to recognise the passage of a catheter and if so at what point during the manipulations ? Does he suffer from pain in the bladder and rectum ?

In the presence of gross loss of motion and sensation neglect of such inquiries may lead us to conclude erroneously that conduction in the spinal cord is completely destroyed. We must also bear in mind that with the severest lesions at the level of the ninth and tenth thoracic segments the sensibility of the stomach remains unaffected, and even a distended bladder may be recognised by the pressure it exerts on the abdominal viscera. Moreover, injury in the mid-lumbar region allows of pain from the trigone, although the remainder of the bladder and ureter are entirely insensitive.

With lesions of the spinal cord and brain-stem it is well to begin by deter- mining the loss of sensibility to prick. But it is important to be certain that when the patient says he " feels the pin " he is really sensitive to the painful aspect of pricking. The majority of the less complete lesions of the spinal cord do not affect tactile sensibility and the power of distinguishing the head from the point of a pin is retained ; thus the patient can recognise contact of the head from that of the point of a pin although he is entirely insensitive to pain on the surface of his body. He must never be asked, " Is that the point of a pin ? " " Am I pricking you ? " ; he should be told before the testing begins to answer " touch," " point," or " pain," and no questions should be put to him during the manipulations. If the observer still remains doubtful whether the patient's answers are really based on the power to appreciate pain, a test-tube containing water at 55° C., or an interrupted current just strong enough to excite pain, can be used as controls.

The extent of the analgesia is first mapped out roughly and its borders are then delimited with greater care. Sometimes a definite line separates the sensitive from the insensitive parts of the body; but more often there is no such absolute hard-and-fast boundary. If this is the case testing should be carried out as follows : start below within the completely analgesic area and work systematically upwards on the body until the patient appreciates

CLINICAL APPLICATION OF THESE METHODS 43

the painful aspect of the prick. Then carry out the test in the opposite direction, beginning over normal parts ; when passing downwards on the body record the boundaries at which the sensation becomes abnormal and those at which all sensibility to pain is lost. The parts which lie between the line of change and the total analgesia form the intermediate zone where sensation is disturbed but not abolished. The extent of this area is of great importance both for diagnosis and prognosis. If the upper border of the analgesia only is recorded on the chart it does not in any way indicate the site of the lesion ; this is revealed more nearly by the line at which sensation changes from normal to abnormal and vice versa.

On the other hand, the more complete the destruction of sensory conduc- tion the smaller will be this intermediate zone; total transverse division of the spinal cord is frequently associated with an analgesic border so definite that it does not vary by one centimetre in either direction.

The algometer for measuring sensibility to painful pressure should never be applied until the close of the examination, and the greatest care should be taken not to cause excessive discomfort. The patient should be told to call out directly the pressure exerted becomes in the least uncomfortable; but the results obtained do not aid greatly in clinical diagnosis, although they are of profound scientific importance.

With lesions of the spinal cord, or brain-stem, sensibility to heat and cold may be disturbed independently of one another. Under such circumstances the principal aim of the thermal tests is to discover whether the patient can recognise the two qualities of sensation; determination of a threshold is of comparatively little importance. We are therefore accustomed to use the large copper tubes containing respectively water at from 2° to 10° C. and from 42° to 48° C. A thermometer thrust through the cork stopper tells the temperature within, which changes comparatively slowly.

But these observations are open to several fallacies. If the temperature of the hot tube is too high the patient is liable to call the " stinging " sensation it evokes " heat," although he may be in reality entirely insensitive to any thermal element in the stimulus. It is difficult to avoid knowledge on his part that he is being tested with heat and cold, and the " sting " of water at from 50° to 60° is so characteristic that, if he is sensitive to pain, he at once recognises that the hot test is being applied. In the same way he may be unable to respond to cold, but can appreciate the disagreeable aspect of low temperatures; this may lead him to call an iced tube " cold" and to dis- criminate it accurately from one containing hot water. In each case the stimulus is named correctly with the help of accessory sensations that have nothing to do with thermal sensibility.

Again, a neutral tube, which is recognised as such over normal parts, may be persistently called either " hot " or " cold " over the affected areas of the body. It is most important, therefore, to interpose frequent stimula- tions with a test-tube which is neither hot nor cold to the normal skin.

44 STUDIES IN NEUROLOGY

Another difficulty arises from the existence of " paradoxical " cold. When a considerable area on the trunk or limbs is insensitive to heat, a temperature of about 45° C. stimulates the cold-spots and evokes a sensation of cold ; but all thermal sensibility disappears when the contents of the hot tube are allowed to sink below about 40° C., although this temperature produces vivid " warmth " over normal parts. This is the well-known phenomenon of " paradoxical cold."

No analogous paradoxical sensation of heat can be demonstrated either on the normal skin or during the course of injuries to the peripheral nervous system. But, when all sensibility to cold is lost as the result of some struc- tural disorder of the spinal cord, and yet heat can be appreciated, temperatures below about 20° C. are not infrequently called " warm." This may be another instance of the tendency to call neutral stimuli " warm," which is so frequently a source of confusion with thermal tests ; or it is possibly due to the existence of paradoxical heat. If this is so the phenomenon is much less vivid and definite than the analogous sensation of cold.

When the lesion of the spinal cord is situated in the cervical or upper dorsal region, the sacral areas on the back of the thighs and calves not un- commonly remain sensitive to pain, heat and cold, or to one or more of these qualities dissociated from one another. Thus the superficial analgesia may be complete on the abdomen and lower extremity, but the third and fourth sacral segments remain sensitive to prick (see p. 386) ; a similar condition existed for thermal stimuli except that the area over which sensation was preserved was somewhat more extensive and included the sole of the foot. Such reten- tion of sensibility over the lower segmental areas is of considerable diagnostic importance and may be easily overlooked.

As a rule there is little difficulty in testing appreciation of the posture of the limbs or the power of recognising passive movements ; for, when this aspect of sensation is affected from some lesion of the spinal cord, the loss is usually extremely gross. The patient may not only fail to appreciate that the leg is being bent or straightened at the knee, but be unable to recognise that it is resting in a flexed or extended position.

The crudest of all the tests for recognition of posture is to place one lower extremity into a certain position and then to ask the patient to touch the great toe with the heel of his other foot. First we make certain that this movement can be carried out accurately, when the eyes are open and attention is directed to the lower extremities. Then the eyes are closed or the lower part of the body is effectively screened. If the power of recognising posture is disturbed the patient finds difficulty in approximating his sound foot to the great toe of the affected limb, but may carry out the opposite movement with comparative accuracy. This is, however, a coarse test and depends greatly on the sensory condition of the joints of the hip and the knee.

When both lower extremities are affected we ask the patient to imitate with his hand the position and movements of the foot we are testing. Thus

CLINICAL APPLICATION OF THESE METHODS 45

with extension or flexion of the great toe he raises or lowers his thumb and indicates by movements at the wrist the posture assumed by the foot. This method is sometimes very successful for diagnostic purposes, but cannot be recorded in measurable terms.

Frequently, when in doubt, the patient guesses at an answer, and if this happens to be correct it is difficult to be certain that there is no appreciation of passive movement. We therefore continue to grasp the part firmly between the fingers, holding it at rest for a time in the new posture. If recognition of passive movement is gravely disturbed, the patient not infrequently describes some fresh change of position, although the part has remained quiescent. Such false answers may be almost as frequent on the records as his replies to actual changes in posture.

Occasionally after a series of observations the limb is held in one position and the patient is allowed to open his eyes; his look and exclamation of astonishment is strong corroborative evidence that his power of appreciating movement and posture is gravely affected.

The tuning fork has long been known as one of the most valuable tests with lesions of the spinal cord ; it is the most easily handled indicator of the functional state of the posterior columns. So long as one lower extremity gives normal answers to vibration, the procedure we adopt follows that laid down in the general chapter on Methods ; but with lesions of the spinal cord the sensation of both legs is frequently affected and we are forced to compare the duration on the sole of the foot with that on the normal palm. This is most unsatisfactory unless the difference is extreme. Fortunately, however, if the loss of sensibility is bilateral, it is usually so gross that the vibration is not appreciated at all.

This test is frequently treated as if it depended on the sensibility of bones and other deep structures only; but when the anaesthesia is bounded by a firm line running from back to front across the abdomen, vibration not infre- quently reveals a similar and definite border. This seems to be particularly evident, when the upper limit of the loss of sensation is due to injury of posterior roots. Under these conditions the tuning-fork may be of considerable use in determining the level of the lesion.

The compass test, though of great scientific interest, is of little diagnostic importance in lesions of the spinal cord. Loss of ability to discriminate two points shows some functional disturbance of the posterior columns, and although this may not be exactly co -extensive with the want of recognition of passive movement or vibration, the differences are of little practical importance.

So long as the lesion is situated within the spinal cord localisation of the stimulated spot is closely associated with the condition of contact sensibility. We have employed as our test the modified Henri method, using a living model of the part under examination, as described on p. 25.

If one or both hands are affected the power of discriminating weight,

46 STUDIES IN NEUROLOGY

form and texture, can be employed as a guide to the finer functional aptitudes depending on the condition of the posterior columns. But lesions of the spinal cord commonly affect the trunk and lower extremities only. Here it is not possible to apply these tests with any hope of obtaining results of any definite value. Some peculiarly intelligent patients can recognise correctly with the soles of their feet the shape of the wooden figures we use for testing forms in three dimensions. But the majority are unable to do so ; this renders these tests of little practical value in most cases of disease or injury t3 the spinal cord.

(3) With Cerebral Lesions. Name —

Address —

Age — Occupation —

Disease or Injury — Date of onset — Cause — Nature — Situation of Injury—

(Exact measurements of situation of wound or opening in the skull.

Retraction, bulging and pulsation of trephine opening) — (Radiographic examination if necessary.)

Mental State —

(Especially state of memory, attention and power of concentration, affective condition and behaviour under examination.)

Sleep and Dreams —

Speech —

Convulsions or Seizures —

Headache —

Character, time of onset, duration —

Effect of posture, movement and vibration (e. g. railway travelling),

fatigue (mental and physical), concentration and intellectual effort — Tenderness (superficial or deep) — Consciousness of the opening or point of injury.

Vomiting —

Vision. (Acuity and Visual Fields.) Ophthalmoscopic examination.

Hearing —

Smell and Taste —

CLINICAL APPLICATION OF THESE METHODS 47

Affections within the territory of the Cranial Nerves — Reaction of the Pupils — Ptosis, or narrowing of palpebral fissure — Ocular movements — Nystagmus — Sensation of the face — Movements of the face — Movements of the jaw — Movements of the palate — Movements of the tongue —

(Condition of Sterno-mastoid and Trapezius if affected) — (Examination of Larynx if necessary.)

Motor Power —

(Recording first the condition of the upper and then of the lower

extremity) — Loss of Voluntary Power —

(Especially individual movements.) Movements which can be carried out voluntarily in the affected

limbs —

Co-ordination with eyes open and shut — Involuntary and Synergic movements — Tremor —

Tone of the affected limbs — Wasting — Gait- Power of standing (on one or both feet; with eyes open and shut.)

Reflexes —

Wrist- jerks —

Triceps- j erks —

Abdominal reflexes —

Knee-jerks —

Ankle- jerks —

Ankle clonus —

Plantar reflexes (observe the action of the inner hamstrings) —

Sensation —

Spontaneous —

" Numbness," Pain, Tingling —

Knowledge of the existence of the affected parts, and conception of their posture.

48

Loss of Sensation —

Touch- Cotton wool or camel's-hair brush over hairless and hair-clad parts — Tactile hairs-- Tickling—

Pain —

Pricking. Threshold with Algesimeter —

Affective reaction to measured pricking and to painful pressure —

Heat and Cold —

Recognition of heat and of cold —

Discrimination of different degrees of heat or of cold —

Neutral zone compared on the two sides —

Affective reaction —

To extreme degrees of heat and cold — To pleasant warmth —

Appreciation of Posture —

Appreciation of Passive Movement —

Falling away of the unsupported limb, when the eyes are closed — Measurement of the angle of the smallest movement that can be appreciated and of the angle at which its direction is recognised correctly —

(Vibration of the Tuning-Fork) —

Compass Test (points applied strictly simultaneously) —

Localisation —

Discrimination of Weights —

With the hands fully supported. Addition and Subtraction — " Weighing " freely —

Discrimination of objects of various shapes —

(Nature of common objects placed in the hand) —

Recognition of Texture —

Sphincters —

Micturition- Defecation —

Surgical Record —

As a rule there is little difficulty in discovering the nature of the sensory disorder caused by a lesion of the spinal cord or brain-stem. No elaborate tests are required ; for the loss of sensation is usually severe and corresponds in great part to the simple categories of touch, pain, heat and cold.

But whenever the lesion lies above the thalamic junction, sensory testing is surrounded by innumerable difficulties. Many of the defects of sensibility appear to be due to a localised loss of attention ; the answers become irregular and the patient appears to be untrustworthy. It is extremely important,

CLINICAL APPLICATION OF THESE METHODS 49

therefore, to exclude all sources of general discomfort, fatigue, or defective concentration. On the other hand, the observer must be expert in adapting his tests to the condition of the subject under examination; a patient whose general powers of attention are poor should not be exposed to an elaborate series of observations, such as a finger to finger examination with the tactile hairs. The tests must be simplified and the area to be explored reduced to the smallest measure compatible with diagnostic information. But if the patient is intelligent, and if his psychical and physical state is favourable, the examination can be extended with due precautions to a remarkable degree.

It is most important to adapt the methods employed to the immediate circumstances ; such tests as the tactile hairs, vibration, and determination of the neutral zone to thermal stimuli should not be deferred to the end of a long sitting, even with the most apt and willing patient. Should the time be too limited for an elaborate series of sensory observations, it is better to choose a few significant tests and to carry them out well rather than to attempt a diffuse and incomplete examination. Hurried testing confuses the patient and destroys that calm so necessary on the side of the observer. With a lesion affecting the sensory cortex, the three tests which yield the most definite results are passive movement, the tactile hairs, and the relative appreciation of graduated weights. Should sensation be disturbed, one or more of these methods of examination will reveal the nature of the defect and, for diagnostic purposes, it is unnecessary to multiply sensory tests.

The condition of tactile sensibility can be roughly explored by a series of contacts with cotton wool. Over the palm of the hand and sole of the foot on the affected side some touches can be appreciated, but others may be missed, although the patient gives a complete sequence of answers from the normal parts. But over hair -clad areas this is not the case; every contact evokes a reply. If, however, the lesion is situated in the optic thalamus, cotton wool moved over the hairs produces a remarkable sensation, usually spoken of as " tingling " or " itching." It radiates widely and is most char- acteristic. But, apart from these indications of some abnormal sensory state requiring further investigation, cotton wool cannot be considered as a ^erious method of examining the condition produced by cerebral lesions. This also applies to the use of the camel's-hair brush.

If a series of pricks with a sharp pin reveal gross loss of sensation, the lesion cannot have affected the cortex only, provided all causes of shock are absent. Either the terminal receptive junction in the optic thalamus has been injured or subcortical paths have been destroyed. But, although the pin is of little value as a test for cortical affections, it is the key to the so-called " thalamic syndrome." When the point is dragged across the trunk from the normal half of the body, an intense over-reaction occurs as it passes the middle line. The patient complains that it " hurts him more," and this is shown by the movements of withdrawal and by the expression on his face. If the palm or the sole are pricked his suffering is obviously greater on the

VOL. I. E

50 STUDIES IN NEUROLOGY

affected side; provided the lesion is confined to the brain, this exaggerated response is diagnostic of thalamic over -reaction.

When sensation is over-weighted with feeling-tone, a similar reaction can be evoked by the large tubes containing broken ice and water at 50° C. or above. Sometimes, by adjusting the temperature of the hot tube so that it falls within the range of pleasant heat, it is possible to show that pleasure is also exaggerated on the affected half of the body ; this is absolutely diagnostic of excessive thalamic activity.

With lesions of the cerebral cortex the most significant thermal test is the discrimination of two temperatures of the same quality, but of different degrees, such, for example, as 35° and 42° C. Both are said to be warm over the hand and foot under normal conditions, but there is no doubt that one is hotter than the other. On the opposite half of the body they may be confused or thought to be identical. When the difference between the two sides is pro- found, this abnormal response is one of the most characteristic signs of a disturbance of thermal sensibility. At the same time it is much more easily and certainly determined than the threshold for heat and cold.

Roughness, tickling and scraping are significant elements in the " thalamic syndrome," but are not otherwise of importance with lesions of the brain.

The power of recognising vibration is of great scientific importance, but has no practical value with cerebral disease or injury. This test is often difficult to carry out successfully, and all the information it affords can be obtained more easily by measuring the range of passive movement, which the patient can appreciate correctly.

To test localisation by our modification of the Henri method is easy to carry out and often acts as a valuable confirmation of the results obtained by the other methods of exploring the spacial aspects of sensation.

The compass test may also furnish corroborative evidence that the sensory disturbance is of the higher type ; but it labours under the disadvantage that it is profoundly affected by any disorder of tactile sensibility and it is not, therefore, a specific test from the cortical point of view.

One of the commonest defects produced by a cerebral lesion is want of recognition of the posture of the affected parts. Not infrequently this can be demonstrated in the following manner. Place the arm in a resting position on the bed and allow the patient to look at it and feel it with his normal hand. Then, having closed his eyes, remove the limb into some different position and ask him to touch a definite digit with his normal index finger. If he has lost the power of recognising posture to any considerable extent, he will grope on the bed in the neighbourhood of the previous position of his hand.

Whenever the faculty of recognising posture is disturbed from a lesion of the brain, the patient experiences greater difficulty in finding the affected limb with the normal hand than vice versa ; it is easier for him to indicate some spot on the normal side with the affected limb, provided it is not too severely paralysed or grossly inco-ordinate. For in the first case he is ignorant

of the site of the object at which he is aiming, whilst in the second he is aware of its situation, although the instrument with which he points is faulty.

This is the exact opposite of the result not infrequently obtained in hysterical conditions ; here it is the affected limb that fails to find the normal one. For, since hysteria proper follows psychical and not physiological lines, it is the affected parts which carry out their functions badly; a " good " limb executes all its movements normally, even when it is set to find a part of the body whose position is presumably unknown to the patient with his eyes closed.

Of all the tests for loss of sensation, measurement of the range of passive movement necessary to excite recognition is the most valuable from the point of view of cerebral lesions. No sensory disturbance is so universal, and the difference between the results, obtained from the normal and affected halves of the body, differ so profoundly that measured movement becomes of predominant importance both diagnostically and scientifically.

The direction of the movement carried out passively is frequently indicated wrongly and the records may be disturbed by hallucinations. These confuse the orderly presentation of the numerical defects, but are in themselves of great importance diagnostically; for they are particularly liable to occur when the lesion affects the cortex, although they may appear with other cerebral lesions.

Ability to recognise differences in the weight, size and shape of external objects depends on one group of cortical activities. Not infrequently the loss of sensation is so gross that the patient cannot recognise the nature of common objects placed in his hand ; under such conditions measurements are not necessary from a practical point of view.

But whenever the disturbance is less severe, an examination with graduated weights is both the easiest and most satisfactory of all these tests. First the hands must be fully supported with the palms upwards in an easy position; two weights are placed successively, first on the normal hand and then on that which is affected. The patient is asked to state which of the two weights is the heavier. Normally there is no difficulty in recognising the difference between 70 and 100 grms. and many persons can give a series of correct answers with 80 and 100 grms. For clinical purposes it is unnecessary that the weights should differ from one another by less than 10 grms.

Then we estimate the power of recognising increase or decrease of a weight resting on the hand according to the method described on p. 32. This is an easy and significant test, provided care is taken to avoid excessive contact stimuli, which are liable to arise from clumsy addition and removal of the weights.

Finally the patient is asked to compare two weights balanced freely one in each hand. So long as the lesion is subcortical, this faculty depends on his capacity to estimate movement, whilst with affections of the cortex the power of " weighing " may be preserved or lost independently of the spacial aspects of sensation.

PART II

THE PERIPHERAL NERVOUS SYSTEM

THE AFFERENT NERVOUS SYSTEM FROM A NEW ASPECT1

BY HENRY HEAD, MJX, F.R.S.,

The conclusions expressed are drawn from investigations carried out in conjunction with

W. H. R. RIVERS, M.D., F.R.S.,

Fellow of St. John's College, Cambridge, AND

JAMES SHERREN, F.R.C.S.,

Surgeon to the London Hospital.

IT has long been recognised, by all who have interested themselves in the problems of sensation, that no view yet advanced of the structure and functions of the afferent nervous system is sufficient to explain obvious facts. The teaching of the anatomist throws little light on the difficulties with which the surgeon is confronted. On the other hand, it is difficult to reconcile the various views concerning the nature of common sensibility with the facts of clinical experience.

Such want of correspondence between observed facts and the prevailing general ideas showed that the distribution and function of the peripheral nerves required reconsideration. In the present paper we shall put forward a new view of the mechanism of sensation, based upon several different lines of research. If we may seem unduly to neglect the work of others, let it be remembered that this paper is introductory to a series of communications, each of which will deal with one aspect of the subject more exhaustively than is possible in a preliminary statement of a new hypothesis.

When the median nerve is divided, sensation is entirely lost over a consider- able part of both the index and middle fingers. Over the palm, within the area said by the anatomists to be supplied by this nerve, sensation is usually dimin- ished and not completely abolished. In a similar manner, division of the ulnar nerve produces complete insensibility of the little finger, and of a variable portion of the ulnar aspect of the palm ; but partial loss of sensation is found over a larger area of the palm and the ulnar half of the ring finger. Such is

1 The substance -of this paper was delivered on May 23, 1905, before the Royal Medical and Chirurgical Society as the Marshall Hall address.

55

56 STUDIES IN NEUROLOGY

the usual statement of surgeons and anatomists. When they are asked, why sensation is only partially lost over the palm, the usual answer is, " Because there the nerves overlap." But if each nerve occupies the territory of the other to an extent sufficient to prevent absolute loss of sensation over so large a portion of the palm, it is obvious that destruction of the ulnar nerve must cause some diminution of sensibility over the median half. This loss should vary exactly in proportion to the amount of sensation that remains, after the median has been destroyed. But the most careful examination of the hand fails to show the slightest diminution in sensation over the median half of the palm in consequence of division of the ulnar nerve. What has always been called the diminished sensibility produced by the division of a nerve is really a condition in which some kinds of sensibility are lost and others retained. Within such a region of altered sensibility all sensation to light touch is abolished. If, in a patient who has divided his ulnar nerve, the ulnar half of the palm of the hand is stimulated with cotton wool, no sensation will be produced, while the lightest touch can be appreciated directly the line corre- sponding to the axis of the index finger is transgressed. If the area is large enough to apply a pair of compasses, it will be found that the patient is totally unable to appreciate two points two centimetres apart. Not only is sensation abolished to these tests, but careful examination shows that temperatures between 22° C. and 40° C. are not appreciated over this area. Thus, parts which have universally been considered to be areas of diminished sensibility turn out to be totally insensitive to certain higher forms of stimulation.

When the hand has settled down after the shock of the injury that has divided one or more of the nerves to the palm, it will be found that, although the area we have spoken of is totally insensitive to certain higher forms of stimulation, a stimulus producing pain, e. g. a prick of a pin, causes a more unpleasant effect than over normal parts.

If the nerve has been united, sensation begins to return after a variable interval. The first sign of recovery is a gradual diminution in the extent of the area insensitive to pain and to all forms of heat and cold.

Finally, no part of the affected hand remains completely insensitive to all cutaneous stimuli. It is to the condition of a hand at this stage of recovery that we wish to draw particular attention. It might be supposed that, with the gradual disappearance of analgesia, an improvement would follow in the higher forms of sensibility. This is not so. The boundary at which light touch is lost is as definite as in the days following the injury, although sensi- bility to pain, to heat and to cold, has vastly improved. In this condition the hand may remain for many months, before light touch begins to be appreciated over parts that lie within the borders of altered sensibility.

Closer examination of parts in this condition shows that, although the hand has become sensitive to pain and to temperature, this sensibility is strangely altered. A prick is appreciated, but produces a sensation that radiates widely over the affected area. It causes unnatural discomfort, and the patient has

THE AFFERENT NERVOUS SYSTEM 57

an uncontrollable desire to withdraw his hand. Moreover, although ice and water at a temperature of 50° C. are appreciated as cold and hot, intermediate degrees produce no sensation of temperature, and water at 25° C. or 26° C. may be indistinguishable from water at 40° C.

We assured ourselves of the truth of these conclusions during more than two years spent in watching patients who had come to the London Hospital on account of injuries to one or more peripheral nerves. But it became obvious, that in order that we might examine more exhaustively the sensory condition of parts that had been robbed of their nerve supply, it was necessary that the patient should be a trained observer, and the injury determined beforehand.

On April 25, 1903, the radial (ramus cutaneous n. radialis) and external cutaneous nerves were divided in the neighbourhood of my elbow, and after small portions had been excised, the ends were united with silk sutures. Before this operation, the sensory condition of the arm and back of the hand had been minutely examined, and the distance at which two points of the compass could be discriminated had been everywhere measured.

This operation produced loss of all forms of cutaneous sensibility over an extensive area on the radial half of the forearm and back of the hand. Stimula- tion with cotton wool, the prick of a pin, the application of all forms of heat and cold, were unappreciated, and the two points of the compasses could not be discriminated, even when separated to the furthest extent possible. But if this part was touched with the point of a pencil, the head of a pin or even with the ball of the finger, the stimulus was at once appreciated, and the point of application localised with remarkable accuracy.

We are thus face to face with the conclusion, that complete destruction of all the sensory nerves to the skin leaves the part sensitive to most of those stimuli commonly used by the physician and surgeon as a test of sensibility to touch. With the Graham-Brown sesthesiometer, an instrument which measures the appreciation of irregularities in an otherwise smooth surface, the hand that had been robbed of all its cutaneous sensibility was found to be actually more sensitive than a similar part on the normal side.

Since 'all the nerves had been divided which supplied the skin, the main- tenance of this sensibility must have been due to afferent fibres running with motor nerves . Sherrington ( 1 1 1 ) has demonstrated the existence of such sensory fibres and traced them to the muscles, tendons and joints. By the operation on my arm, we had gained the unique opportunity of exposing a part, endowed with deep sensibility only, to a series of careful tests.

The peculiar aptitude, possessed by a part innervated solely by the afferent fibres of a muscular nerve, is the appreciation of all stimuli which produce deformation of structure. Pressure or any jarring of the skin was quickly appreciated in my case, and, on the whole, was localised with remarkable accuracy. But, when the hairs were pulled, the elevation of the skin produced no effect upon consciousness. Pressure, which had previously caused a sensa- tion, was no longer appreciated when applied to the skin lifted from the subcu-

58 STUDIES IN NEUROLOGY

taneous structures to form a ridge. This showed that the sensibility to pressure was not due to nerves still remaining in the skin after the operation. Although pressure was localised with considerable accuracy, all sense of form and size was lost over the parts affected. The prick of a pin and the interrupted current were entirely unappreciated; but excess of pressure produced aching pain. When the pressure was produced by means of Cattell's algometer, it was found that pain was elicited with a smaller pressure of the instrument than on the sound side. The affected parts could be burnt without producing pain, and no sensation of cold was produced, even when the hand was frozen firmly by means of ethyl chloride.

This condition remained unaltered until seven weeks after the operation, when sensation of prick began to return on the arm. Six weeks later, there was no part of the forearm where prick could not be appreciated, and within 200 days from the time when the nerves were divided, even the back of the hand had become sensitive to this form of stimulation. Yet, for more than a year, both forearm and hand remained completely insensitive to light touch, and more than two years after the operation, the hand had not completely regained its sensibility, when tested with cotton wool and with the compasses.

Thus, we had ample opportunity of examining with care the sensory con- dition of a part sensitive to prick, but insensitive to light touch. We found that, when the forearm or hand was pricked, the pain produced was not localised, but radiated widely, and was not infrequently referred to some part at a distance from the point stimulated. Ice and water at 50° C. were appreciated, but minor degrees of temperature produced no effect upon consciousness. This peculiarity in the behaviour of the hand and forearm we found to be due to what are known as " cold- " and " heat-spots."

Blix (7 and 8) first described the presence of " cold -spots " in the skin, and his work was amplified by Goldscheider (40). To some observers, such as von Frey (32 to 36), all forms of sensation possessed by the skin are due to the existence of small areas of specific sensibility. So extreme a view has been accepted by few ; some even doubt the very existence of temperature spots. By suitable methods spots can be demonstrated in the normal skin where cold alone can be appreciated ; analogous spots, more sparsely scattered, can also be shown to be devoted entirely to sensations of heat. In the same way it would seem that there are spots peculiarly sensitive to the prick of a sharp needle ; but the disturbance produced by their stimulation is so great, that they cannot be demonstrated with the same certainty as the spots devoted to sensations of temperature. Now pari passu with the return of sensibility to prick and to the extremes of heat and cold, these spots reappeared upon my arm and hand. But whereas, in the normal skin, the heat- and cold-spots are nothing more than minute areas peculiarly sensitive either to heat or to cold, set in a territory over which temperature stimuli can also be appreciated, the spots which made their reappearance on my arm during the first stage of recovery were set in an area insensitive to temperature stimulation. Thus, they were not only dis-

59

coverable with unusual ease, but, since the only form of temperature sensation possessed by the recovering part was due to their presence, it was particularly easy to investigate their sensory peculiarities. The cold-spots could be stimu- lated by any temperature below about 24° C. ; but, whenever a spot reacted, what might be called an explosion of cold was produced, not localised at the point touched, but radiating widely, sometimes even to a very considerable distance. A small group of spots on the wrist always produced a sensation of cold in the forearm just below the fold of the elbow, and two spots in the forearm, when stimulated, evoked a sensation of cold in the thumb. The heat-spots, more sparsely scattered, behaved in a similar manner. The lower limit of temperature to which they reacted varied from 38° C. to 45° C. One extremely sensitive spot even reacted to 37° C. But, whether these spots reacted slowly or briskly, the sensation was always one of widespread heat, and, until the painful limit of heat was reached, it mattered little at what temperature the stimulus was applied, provided it lay within the limits capable of stimulating these spots. The following experiment, which demonstrates this peculiarity, was many times repeated with the same results. A cold -spot of unusual activity was stimulated by means of a copper cylinder of one millimetre diameter, cooled to the temperature of melting ice. This produced a sensation of cold. Water at 20° C. was placed in a test tube with a flat bottom of one centimetre diameter, and this was applied to the skin in such a way that it stimulated a constellation of spots, among which lay the spot originally stimulated. The sensation of cold produced by this stimulus was more intense than that produced by stimu- lating a single spot with a temperature considerably lower. Thus we come to the remarkable conclusion that the heat- and cold-spots are incapable of produc- ing, in consciousness, graduated sensations of heat or of cold. Water at 20° C. can be made to appear colder than ice, provided the stimulus is so arranged that the former is applied over a considerably larger area than the latter. Such spots resemble in their action the cold alarms of our greenhouses. When the temperature falls below a certain amount, a bell is rung, but no indication is given of the extent to which the temperature has fallen.

Although we had peculiar difficulty in demonstrating the presence of similar spots for pain, the general behaviour of a part in this stage of recovering sensibility, closely resembles that of the heat- and cold-spots. Radiation takes place widely ; a more intense stimulus is necessary to evoke pain, but when evoked, the pain is greater than over the normal skin. We also found that in this stage of recovery many of the hairs had gained a peculiar sensibility. When a hair on the normal skin is gently lifted, a sensation of touch is caused which is extremely well localised. But in the stage of recovery we are now dis- cussing, the movement of the hairs produced a curious widespread formication, with the same reference to distant parts as in the case of temperature and pain.

However widespread the radiation may be to prick, to heat, to cold, or on touching the hairs, it is not fortuitous in its distribution. We found, by

60 STUDIES IN NEUROLOGY

repeated experiment, that certain areas on the hand always caused radiation into some other part irrespective of the form of stimulation.

All these facts would seem to show that we are here face to face with an undiscovered form of sensibility, capable of producing qualitative changes in consciousness, but incapable of causing a quantitative change apart from the extent of area stimulated. The position of the point stimulated cannot be recognised and each stimulus causes a widespread, radiating sensation, not infrequently referred to parts at a distance. To this form of sensibility we propose to give the name " protopathic."

The return of protopathic sensibility brings a cessation of all those destruc- tive changes in nutrition that occur in parts where the skin is insensitive. Ulcers form, as the consequence of burns or cuts, and do not heal so readily as on the normal skin. But such trophic changes are confined to parts insensitive to protopathic stimuli. With the return of protopathic sensibility, ulcers cease to form, and sores heal as readily as on the normal skin, although the parts remain insensitive to all the higher forms of stimulation, such as light touch. Thus a part supplied by protopathic sensibility alone, grows and is repaired, as easily as the normal skin.

After the affected part has remained for a variable period in this condition, it begins to become sensitive to light touch, and degrees of temperature, which produce the sensations called " warm " and " cool " on the normal skin, are again distinguished correctly from one another. With the gradual return of sensation, it again becomes possible to discriminate two points touching the skin at distances more nearly normal, and the widespread radiation, so charac- teristic of the first stage of recovery, ceases, and is replaced by an increasing accuracy of localisation. To this form of sensibility we propose to give the name " epicritic," since it is peculiarly associated with the localisation and discrimination of cutaneous stimuli.

So far we have demonstrated the existence in the skin of two forms of sensibility, but have brought forward no evidence to show that they depend upon anything more than modifications of the same system of nerve fibres and end-organs.

I can now deal with a curious phenomenon that occurred in the case of my arm. Over the radial half of the dorsum of the wrist, a triangular area of skin became entirely insensitive to prick in consequence of the operation. But this same area remained sensitive to touches with cotton wool, and also, in a limited degree, to warmth. The area was small, and its epicritic sensibility was of a low order ; but in spite of these disadvantages, repeated testing seemed to show that the area was capable of responding to temperatures between 42° and 48° C.1 It was, however, entirely insensitive to temperatures of 50° C. and above. To ice and to all forms of cold, this part was equally insensitive. It would therefore seem that, by a fortunate chance in nerve distribution, we had divided those fibres which subserved protopathic sensi- 1 See p. 285 for a fuller account of the condition of the triangle.

THE AFFERENT NERVOUS SYSTEM 61

bility, leaving untouched, at any rate, some of those which conducted the impulses of epicritic sensibility. Such an observation can only be explained -' by assuming that the two forms of sensibility depend upon two separate systems in the peripheral nerves. Experiments with so delicate a sensory change can, only be carried out satisfactorily by frequent repetition, by selection of occasions when the subject is, from the sensory point of view, in excellent condition, and under the rigid check of a large number of controls. These conditions are rarely, if ever, satisfied during the examination of patients in whom the loss of sensation has been produced by accident.

The mode of recovery of sensation after injury to a peripheral nerve also supports the view, that these two forms of sensibility depend upon separate structures. If the nerve has been completely divided, protopathic sensibility returns first, followed at a considerably later period by return of epicritic sensation. Provided the nerve has been completely divided, we have never seen the faintest sign of returning epicritic sensibility, unless sensation to prick had already shown material improvement. But, if the nerve is only bruised or injured, so that its continuity is functionally, but not structurally, destroyed, the two forms of sensibility may return pari passu.

Evidently, the two systems regenerate with unequal facility. The proto- pathic system regenerates more rapidly and with greater ease. It can triumph over want of apposition and the many disadvantages that are liable to follow traumatic division of a nerve.

Moreover, the length of the nerve to be regenerated makes relatively little difference to the time at which protopathic sensibility returns. Although the nerves in my arm were divided at a point at least 20 cm. above the wrist, recovery began in seven weeks and was completed, even over the hand, in twenty-nine weeks. This compares favourably with most of our instances of primary suture, in which the nerve was divided at the wrist. But this is in no way true of the epicritic system. Provided the wound is healthy, and the operation of the primary suture has been successfully performed, the length of time required for epicritic regeneration depends upon the distance of the wound from the periphery. And this is why, in my case, the period between the close of the first stage and the beginning of the second stage of recovery was unusually prolonged.

Every peripheral nerve contains in varying proportion the fibres subserving these two forms of sensibility. Let us consider for a moment their distribution in the nerves, the trunks and the roots which supply the upper limb.

To simplify what must of necessity be a somewhat complex statement, I will deal first with the supply of epicritic sensibility only. On the palm of the hand, the area supplied by the ulnar and median nerves overlaps to an extent less than one -half the breadth of the finger. Consequently, the borders of the insensitive area produced by division of one or other of these nerves is well defined. The back of the hand can be roughly divided into two halves, by a line running from the knuckle of the middle finger to the middle of the back

62 STUDIES IN NEUROLOGY

of the wrist. On the ulnar side of this line, the hand is supplied by the ulnar and internal cutaneous, on the radial side by a combination of external cutane- ous, the radial and the long cutaneous branch of the musculo -spiral. If we now include the forearm, it will be found that a line drawn up the flexor surface continuous with the axis of the ring finger, and up the extensor surface, continu- ous with the line just mentioned on the back of the hand, divides the whole of the forearm and hand into a pre-axial and a post-axial portion. Of these the post-axial portion is supplied by the ulnar and internal cutaneous, the pre-axial portion by the median, the radial, the external cutaneous, and the long branch of the musculo -spiral.

Another border, which has the same character as these two axial lines, is the boundary separating the distribution of the median from that of the group of nerves supplying the radial half of the dorsal surface of the hand.

Whenever division of any nerve branch causes loss of sensation to light touch along one of these lines, that border will be well defined. Division of one branch only will produce no definite area of anaesthesia, unless that area is bounded by one or more of these lines.

Thus, provided the peripheral nerves are gathered into certain groups, it may be said that from the point of view of light touch, and other forms of epi- critic sensation, very little overlapping occurs. These groups are as follows : (1) The ulnar and internal cutaneous; (2) the median; (3) the remainder of the pre-axial group.

From this arrangement, the distribution of protopathic sensibility differs fundamentally. Enormous overlapping occurs, as we have already seen from a consideration of the analgesia caused by division of the median or of the ulnar nerves. Evidently, the peripheral nerves, looked at broadly, form the units of epicritic supply. On the contrary, from the protopathic point of view, no one nerve forms anything more than a tributary supply of an area innervated by a plexus of nerves, and, whenever a single peripheral nerve is destroyed in the upper limb, the loss of light touch always exceeds considerably the extent of the loss to prick. But, as soon as we have to deal with destruction of the cords of the brachial plexus, the extent of the analgesia almost equals that of the loss to light touch ; and, when several posterior roots have been divided, the extent of the area insensitive to prick may actually exceed that insensitive to light touch. Thus it is evident that, whilst the unit of supply for epicritic sensibility, looked at broadly, lies in the peripheral nerves, the unit of proto- pathic supply lies in the posterior roots. The more nearly a peripheral nerve represents the supply of one or more posterior roots, the more definite will be the borders of the analgesia produced by dividing that nerve. The median nerve probably contains sensory fibres from the seventh and eighth cervical, and possibly even from the sixth cervical and first dorsal. Destruction of this nerve will therefore only cut off protopathic sensibility from the compara- tively insignificant area to which all the fibres from these roots run in the one nerve. On the contrary, the distribution of the external popliteal, including

THE AFFERENT NERVOUS SYSTEM 63

\ts lateral cutaneous branch, corresponds closely to that of the fifth lumbar root. Consequently, destruction of this nerve produces a widespread loss of sensation to prick, with an extremely well-defined border on the shin and dorsal surface of the foot.

The sensory mechanism in the peripheral nerves is thus found to consist of three systems :—

(I.) Deep sensibility, capable of answering to pressure and to the movement of parts, and even capable of producing pain under the influence of excessive pressure, or when the joint is injured. The fibres, subserving this form of sensation, run mainly with the motor nerves, and are not destroyed by division of all the sensory nerves to the skin.

(II.) Protopathic sensibility, capable of responding to painful cutaneous stimuli, and to the extremes of heat and cold. This is the great reflex system, producing a rapid widely diffused response, unaccompanied by any definite appreciation of the locality of the spot stimulated.

(III.) Epicritic sensibility, by which we gain the power of cutaneous localisa- tion, of the discrimination of two points, and of the finer grades of temperature, called cool and warm.

Let us now pass to the consideration of the arrangement of sensation in the central nervous system. The view I shall put forward is based upon the examination of a series of cases of haemorrhage into the spinal cord, and of injuries affecting its substance, producing what is usually known as Brown- Sequard paralysis. With these we have compared the sensory changes in syringomyelia and tabes dorsalis. Now, all these conditions demonstrate that, as soon as a sensory impulse reaches its first junction in the spinal cord, it becomes shunted into tracts devoted to the conduction of impulses, grouped in a way different from that found in the peripheral nerves. It is no longer a question of protopathic, epicritic, or deep sensibility ; the tracts in the central nervous system are devoted to the conduction of impulses concerned with pain, heat, cold, and touch.

Thus, in Brown-Sequard paralysis, motion is lost in the one limb, and all sense of pain, heat or cold, is abolished in the other. Careful examination of this loss of sensation shows that sensibility is equally lost to all forms of tem- perature stimulation, and that we have here to do with no such separation into extreme and intermediate degrees as exists in the peripheral nerves.

In the central nervous system, the impulses are co-ordinated and distributed, just as in the central office of a newspaper the various accounts of the same event, arriving by telephone, by tape, or by telegraph, are co-ordinated and distributed according to their subject-matter.

It has long been recognised, that the viscera are not endowed with the same sensibility as the skin, and some have even questioned whether they are sensi- tive at all. It is certain, from the observations of Lennander (66) and his school, that the patient shows no sign of pain when the gut is incised, or even when it is burnt; the liver is also apparently insensitive to similar injuries,

64 STUDIES IN NEUROLOGY

and yet everyone is agreed that the parietal peritoneum is highly sensitive. We determined to attack the problem from a somewhat different point of view. When a colotomy has been performed, the upper end of the gut opens freely upon the surface, and no faeces pass into the lower portion. It is therefore possible to wash out the lower gut, and by passing a tube into its upper end to apply heat and cold to what is now an isolated loop of intestine. By choosing patients who were intelligent, and such as were not cachectic or wasted from malignant disease, we obtained the following result. Water at 40° C. and at 20° C., which seemed warm and cold respectively to the skin of the abdomen, were entirely unappreciated when applied within the walls of the gut. But ice water was at once called " cold," water at 50° C. was said to be uncomfort- able, and two patients of unusual intelligence spoke of this stimulus as " hot." This sensation of heat and cold was never localised in the abdominal cavity. If the patient was asked to indicate the position of the stimulus, he either placed his hand over the region of the navel or pointed into the air. Sometimes the sensation was said to be like cold drops on the skin in a part of the abdomen where it would have been impossible for any water to have fallen. Moreover, the strictest precautions were taken to insert the tube through a ring of mucous membrane and to surround both the tube and funnel with absorbent cotton wool, so that no moisture could possibly escape.

These experiments are not conclusive, but they seem to show that, in some ways, the sensibility of the viscera closely resembles that which we have called protopathic. Only, the extremes of heat and cold are recognised, and localisa- tion is so defective that the patient cannot even tell whether the cold is in or outside his abdomen.

Many of the afferent impulses from the viscera produce a reflex action without affecting consciousness. When we had passed a varying quantity of warm water into the gut, the patient complained that he wished to defsecate ; a reflex peristalsis had been set up of which he was conscious, although he failed completely to recognise the stimulus by which it had been evoked. Most of the afferent impulses from the stomach and intestines probably belong to this order.

To a certain extent, we seem able to appreciate the muscular movements of an internal organ, such as the stomach or intestine, even although we cannot recognise the position in space of the part that is moved. This power is prob- ably the equivalent of that deep sensibility which remains to a part deprived of all its cutaneous sensory nerves.

Structurally, we know that the viscera are innervated from the sympathetic system, and from a set of large afferent fibres connected with the end-organs of Pacini. The latter so closely resemble the mechanism found in muscles, tendons and joints, subserving what we have called deep sensibility, that we can assume the end-organs of Pacini to be the means by which we gain a similar power of appreciating intestinal movement.

But apart from such sensations of movement, the viscera certainly set up

THE AFFERENT NERVOUS SYSTEM 65

afferent impulses which may affect consciousness. We have attempted to show that, however feeble these sensations may be in consequence of the defec- tive inner vation of the intestine, they produce upon consciousness an effect resembling that of a low form of protopathic sensibility. Now, one of the peculiarities of protopathic sensibility is the rapid restoration of the mechanism upon which it is based. This it shares with the sympathetic system. More- over, when a peripheral nerve to the hand is divided, it is noticeable that the palm begins again to sweat at a time after union which coincides approximately with that of the return of protopathic sensibility. This sweating is due to the motor fibres of the sympathetic (the " autonomic fibres " of Langley) that supply the skin.

It will therefore be no adventurous guess to suppose that the system we have called protopathic in the skin is one with the afferent fibres of the sympa- thetic as they supply the viscera. In both cases the sensation is badly localised, radiates widely, and is frequently referred to parts other than those stimulated . Both systems are incapable of appreciating light touch, and both are insensitive to the minor degrees of heat and cold. Both regenerate with the same rapidity and completeness.

We wish, therefore, to put forward a new conception of the nature of the afferent fibres in peripheral nerves.

The whole body within and without is supplied by the protopathic system. The fibres of this system in the skin may be spoken of as somatic, those to the internal organs as visceral protopathic fibres. Thus we shall no longer speak of the afferent sympathetic system, but of the protopathic supply of the internal organs.

Another set of afferent fibres peculiarly associated with impulses of move- ment and pressure exist in connection with the Pacinian organs. In the body and limbs, an analogous system is found peculiarly susceptible to pressure, to the localisation of movement, and to the appreciation of position. The fibres of this system run in conjunction with the motor nerves.

In addition to these two systems, which are distributed to all parts of the body within and without, the surface of the body only is supplied by a third system, which we have called epicritic. This endows the skin with sensibility to light touch. To the impulses conducted by this system we owe the power of localising the position of cutaneous stimuli, of discerning the doubleness of two points, and of discriminating between minor degrees of heat and cold, and other special attributes of sensation. The fibres of this system are more easily injured, and regenerate more slowly, than those of the protopathic system. They are evidently more highly developed, and approach more nearly to' the motor fibres that supply voluntary muscle, in the time required for their regeneration.

VOL. i.

THE CONSEQUENCES OF INJURY TO THE PERIPHERAL NERVES OF MAN

BY

HENRY HEAD, M.D., F.R.S.,

AND

JAMES SHERREN, F.R.C.S.,

Surgeon to the London Hospital. PREFACE

GENERATIONS of anatomists have studied the course and distribution of the peripheral nerves, until knowledge of their more obvious features has apparently reached finality. It is recognised that more can be learnt of their central connections and of the relation of the larger branches to the anterior and posterior roots. But the peripheral distribution of the nerves of the hand is regarded as one of the commonplaces of anatomy.

And yet, whenever an attempt is made to apply this knowledge to some case where one of these nerves has been divided, obvious facts remain unex- plained, or accessory hypotheses must be invented to account for the apparent difficulties of each individual instance. The more carefully the condition of the affected part is examined, the less does the state of its sensibility correspond with the surgeon's expectation. After he has successfully reunited the ends of the nerve, a conscientious examination only adds to the bewilderment of the observer.

If, for instance, the median nerve is divided, all cutaneous sensibility is abolished over a considerable part of both the index and middle fingers. But over the palm, within the area supplied by the median nerve, sensation may be diminished only. In a similar manner, division of the ulnar nerve produces complete insensibility of the little finger and of a variable portion of the ulnar border of the palm. Cutaneous sensibility is only partially lost over the palm and that part of the ring finger usually assigned to the ulnar nerve. When the surgeon or anatomist is asked why sensation is only partially lost, the usual answer is, " Because the nerves overlap." But, if each nerve occupies the territory of the other to an extent sufficient to prevent absolute loss of sensation over so large a part of the palm, it is obvious that destruction of the ulnar nerve must cause some diminution of sensibility within the median area. This loss

INJURY TO THE PERIPHERAL NERVES 67

should vary exactly in proportion to the amount of sensation that remains over this part of the palm, after the median nerve has been destroyed. But the most careful examination of the hand fails to reveal the slightest diminution of sensation over the median half of the palm, in consequence of division of the ulnar nerve. What has always been called diminished sensibility ends sharply at a line in the axis of the ring finger.

Such want of agreement between anticipated effects and the actual results of division of a peripheral nerve pointed to a gap in our knowledge of the distri- bution and functions of this part of the nervous system, which we have attempted to fill.

To those who have not worked in a town like London, it may seem an easy matter to examine a patient with some nerve injury at regular intervals from the date of the accident up to complete recovery. But any systematic attempt to carry out such an investigation is hampered by innumerable difficulties, due solely to the conditions of life among the working population of this huge city. Firstly, the original wound may have been treated at some other hospital, or by a private practitioner. Often the state of the wound and the extent of the injury can then be inferred from the patient's description only. Again, after the nerve has been successfully reunited, he may find it more convenient to attend some other hospital ; or may leave his hand entirely untreated, and thus render useless the careful investigation at the time of the injury, the exploration of the wound at the time of suture, and the observations made during his stay in hospital.

Lastly, the investigation may be brought to a sudden end by his change of dwelling. For instance, within the space of twelve months, one of our patients, a married man with a family, changed his address five times. Two or three changes in a year are of frequent occurrence, and letters remain unforwarded. In spite of the help of an assistant, skilled in tracing the movements of hospital patients, and in spite of the fact that compensation on an ample scale was given for travelling expenses and loss of time, many patients disappeared entirely, often at the most interesting period of recovery. This is particularly liable to occur when the median has been divided. For this injury interferes little with the grasp of the hand, and the patient is afraid to attend the hospital, lest his employer should consider him unfit for work. To meet this difficulty, we found it necessary to institute frequent Sunday sittings.

No instances are included in this paper that have not been examined by one or both of us. As far as possible, one or other of us has been present during the operation; but occasionally we have been compelled to rely on the account given by others of the condition then found. With this exception, no note has been included that is not the direct outcome of our personal observation.

CHAPTER I

NERVE SUPPLY OF THE PALM OF THE HAND 1 8 1. — DIVISION OF THE ULNAR NERVE

o

COMPLETE division of the ulnar nerve in the forearm above the point at which the dorsal branch is given off produces the following changes in the sensibility of the hand.

Touch, prick, heat and cold are no longer appreciated over the little finger and over the ulnar border of the palm. The extent of this absolute loss of cutaneous sensation varies in each individual, and in no two cases is it exactly the same. In one extreme form it may occupy the little finger, one-half of the rinsr finger and more than one-third of the palm and dorsum of the hand, or

0 o •*-

sensation may only be completely lost over the little finger and ulnar border of the palm.

When the whole ulnar nerve is divided, the area of absolute loss of cutaneous sensation lies between these two extreme limits, the amount of loss varying with each individual. And it is this loss of sensation only which can be recog- nised by pricking the hand with a pin. If one finger and a half are insensitive to a prick, the surgeon is satisfied that he has to deal with a " normal " ulnar " completely divided " ; when only the little finger is insensitive, he doubts whether the nerve is completely divided, or looks upon it as abnormally distributed.

But in reality, the sensibility of the hand is disturbed over an area consider- ably greater than that marked out by the analgesia ; and, if cotton wool is used as the test for sensation, touches, easily felt elsewhere on the hand, will not be appreciated over the whole of that portion assigned by anatomy to the supply of the ulnar nerve. This area is bounded by a line running through the longitudinal axis of the ring finger back and front, continued on the dorsal and palmar aspects of the hand to include the greater part of its ulnar half.

The whole of this border can be marked out easily with cotton wool, for, as soon as it is passed, the patient appreciates touches that previously caused no sensation, and, if he is intelligent and quick, the passage from the insensitive to the sensitive area is found to take place at a line which varies very little, whether the stimuli progress is an orderly series from the ulnar to the radial side of the hand, or vice versa.

1 For the extent of the nerve supply of the hand determined by the method of residual sensibility, vide p. 114.

68

INJURY TO THE PERIPHERAL NERVES 69

Thus, by using cotton wool as a test, sensation can be shown to be lost at a line corresponding to the anatomical border of the ulnar nerve.

But there are other means of showing that sensation becomes defective at this border. If a needle or pin is dragged lightly across the skin from the sound to the affected half of the hand, the patient complains that the " feeling " it produces changes as soon as this line is passed. This line can also be marked out by an interrupted current applied in the following manner : Connect one pole of the secondary coil with a large indifferent electrode, and the other pole with a small electrode covered with wash-leather set in a handle containing a key, so that the current can be thrown in and out at will. Remove the iron core from the primary coil, then place the secondary coil at such a distance from the primary, that the current applied through the smaller electrode is easily appreciated on the normal skin. Even though it may be strong enough to contract the small muscles of the thumb, such a current will not be appreciated over the area within which sensation is lost to cotton wool.

Sensation to temperature also undergoes a change at the same border. A test tube containing water at about 22° C., and one containing water at about 40° C., cannot be discriminated, though easily appreciated as cool or warm over the normal skin.

Thus, division of the ulnar nerve produces complete loss of sensation to pain and temperature over the little ringer and over a variable extent of the palmar and dorsal surfaces of the ulnar border of the hand, rarely corresponding even approximately to the anatomical borders of the ulnar nerve. But these borders are accurately marked out by loss of light touch (cotton wool), and of minor degrees of temperature and by inability to appreciate the interrupted current applied in a definite way.

Between the boundaries of this loss of light touch and those of complete loss of cutaneous sensibility lies a territory within which sensation is profoundly changed. The extent of this area varies in each individual case. If the inter- mediate zone be of considerable size, so that the condition of sensation within it is easily investigated, then it will be found that not only is all sensation abolished to light touch, to intermediate degrees of temperature, and to a certain form of interrupted current, but painful stimuli produce an effect different from that upon the normal skin. As soon as the anatomical border is transgressed towards the ulnar side, a prick may become so disagreeable that the patient immediately withdraws his hand. He complains that it causes a feeling of " pins and needles," not only at the point pricked, but also widely over the intermediate zone. Asked to localise the spot pricked, he may be able to do so, but complains that the pain produced seems to him to be spread over a large surface, or even to be in two places at once, such as the base of the finger and the middle of the palm. Moreover, when tested with compasses, the points cannot be distinguished as causing two sensations, even when separated from one another to the greatest extent possible within the inter- mediate zone. An interrupted induced current, with no iron in the circuit,

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cannot be appreciated within this area, but, if bare metal points are used, or if the iron core is inserted into the primary coil, the stimulus causes pain, even when the distance of the coils is adjusted to compensate for the increase of strength produced by the presence of the core.

Thus, complete division of the ulnar nerve above the dorsal branch produces the following changes : —

(1) Loss of sensation to pain, to extremes of heat and cold (ice and water at 50° C.), and to painful interrupted induced currents over an area that may vary greatly in size ; sometimes it includes the little finger, the ulnar half of the ring finger, and more than one-third of the palm and dorsal surface ; in other cases it is reduced to the little finger and a strip on the extreme ulnar border of the hand.

(2) The patient is unable to distinguish two widely separated compass points, or to appreciate light touch, minor degrees of temperature, and the painless interrupted current over an area occupying the. little and ulnar half of the ring fingers, and that part of the palm and dorsum of the hand on the ulnar side of an axial line drawn longitudinally through the ring finger. This corre- sponds to the border laid down by anatomy for the supply of the ulnar nerve.

(3) The sensibility of the intermediate zone on the palm, the dorsum and the ring finger may be characterised by an increase in the discomfort produced by painful cutaneous stimuli, and by a wide diffusion and want of localisation in the sensation produced by a prick.

§ 2. — VARIATION IN THE EXTENT OF THE AREA SUPPLIED BY THE ULNAR

NERVE

Complete division of the ulnar nerve produces loss of sensation to light touch over the whole of the little finger and over some part of the ring finger back and front. In no instance was the sensibility of the ring finger to light touch entirely unaffected. Of nine cases in which the nerve was proved at the operation to have been divided, this ansesthesia occupied the ulnar half of the ring finger in six, and this may therefore be taken to represent the usual supply.

On the palm, the loss of sensation to light touch may occupy a border directly continuous with the axis of the ring finger, or may swing out as far as a line drawn from the cleft between the middle and ring fingers (fig. 5).

Out of these nine cases loss of light touch occupied half the dorsal surface of the ring finger in six ; in one, a third of this finger was affected. In one instance, this anaesthesia occupied two-thirds of the ring finger.

On the back of the hand, the border of the area insensitive to light touch usually follows a line continuous with the axis of the ring finger, but in two cases it swung out to the radial side to reach the tendon of the middle finger.1

1 Under certain circumstances the presence of hairs on the dorsal surface of the hand may make the determination of this border untrustworthy unless the hand be shaved (vide p. 156).

INJURY TO THE PERIPHERAL NERVES 71

To show the loss of sensation produced by complete division of the ulnar nerve. Loss of all forms of cutaneous sensibility is represented by the black area. The parts insensitive to light touch and to the intermediate degrees of heat and cold are enclosed within the black line.

Most of the cases will be found on Table II., p. 92.

A is the loss of sensation in Case 18; B. Case 17; E, Case 16; F, Case 14; G, Case 15; I, Case 19 (also reported on p. 207). The case from which C was taken (No. 83) will be found reported on p. 208; that where the loss of sensation was represented by H, on p. 210 (No. 63). D was taken from a man in whom the ulnar nerve had been divided ; secondary suture was performed, and he was not seen again until complete recovery had occurred.

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The ulnar nerve is usually divided by a transverse cut in the neighbourhood of the wrist, which must also sever some of the branches of the internal cutanous nerve descending to supply the hand. Thus, in most cases, the scar bounds the upper or central border of loss to light touch, and it is only where the ulnar nerve has been injured at the elbow, or high in the forearm, that the true upper limit of the ulnar supply can be determined. Six such cases have come under our notice, in four of which this upper limit ran round the wrist at the level of the styloid process, and in two it formed a curved line about 1 cm. on the distal side of this point. Evidently, as far as light touch is con- cerned, division of fibres of the internal cutaneous nerve plays little part in the form usually assumed by this border after division of the ulnar nerve at the wrist, excepting when the anaesthesia is bounded definitely by the scar.

Thus, the extent of the loss of light touch produced by division of the ulnar nerve seems to be remarkably constant, and it varies, if at all, within small limits only. The borders of this area are definite ; it does not merge gradually, but passes abruptly into parts of normal sensibility.

The area of insensibility to pain, produced by division of the ulnar nerve, differs fundamentally in every characteristic from the condition of parts insensitive to light touch. For, not only is the extent of the loss of sensation subject to great variation, but the difficulty in determining the amount of this variation is increased by the indefinite nature of the borders of the analgesic area. At no point can it be said that here loss to pain begins ; complete sensi- bility to pain merges gradually into complete insensibility with no sharp dividing line, and all attempts to mark out circumscribed areas of analgesia are therefore unsatisfactory. But, taking into account solely the area of total loss of sensation to prick, the only certain result of complete division of the ulnar nerve is to produce analgesia over the little finger and ulnar border of the hand. None of our cases failed to show at least so much loss to prick. But, in extreme instances, sensation to prick may also be lost over the ulnar half of the ring finger and over an area on the palm and dorsum of the hand almost co-terminous with the full ulnar loss of sensation to light touch. It is in such cases that the surgeon, using a pin as his test for sensibility, finds that loss of sensation occupies exactly the area he expected.

Between these two extremes, every form of variation exists ; in no two cases is the extent of the complete analgesia exactly the same, and so diverse are the forms assumed by this loss of sensation that no form can be said even approxi- mately to represent the normal. We have therefore represented the extent of the loss, in each case, in the form of a series of diagrams, from which it will be seen how great may be the variation (fig. 5).

Apparently, the extent of the area insensitive to light touch, and that of the area of absolute loss of sensation to prick, vary independently of one another. A large extent of the ulnar half of the hand may be entirely insensi- tive to pain, and yet the extent of loss to light touch in no way exceeds that found when the analgesia was confined to the little finger. For this reason,

INJURY TO THE PERIPHERAL NERVES

73

the extent of the intervening zone of defective sensibility varies greatly. Its characteristics are an imperfect discrimination of two compass points and an inability to transmit light touch and degrees of temperature between about 22° C. and 40° C. It is, however, sensitive to pain, to ice, and to temperatures above 45° C. But, in consequence of the ill-defined borders of this total loss of sensation, the intermediate zone may sometimes be an area of very defective sensibility, or it may be sufficiently large and sensitive for careful and certain examination of its sensory peculiarities.

§ 3. — Loss OF SENSATION PRODUCED BY DIVISION OF THE ULNAR NERVE, WHEN ITS DORSAL BRANCH REMAINS INTACT

When the ulnar nerve is divided at the wrist, its dorsal branch not uncom- monly escapes uninjured. Such an accident makes it possible to determine the extent to which each of the two branches supplies the ulnar area of the hand.

FIG. 6.

To show the loss of sensation produced by division of the ulnar nerve below its dorsal branch. The area of total loss of cutaneous sensibility is marked in black. The parts insensitive to light touch and to the intermediate degrees of heat and cold are enclosed within a black line.

Both these cases will be found on Table II. B, p. 94. A represents the loss of sensation in Case 20 ; B the loss of sensation which preceded and immediately followed secondary suture in Case 24.

When the dorsal branch is intact, the border of loss to light touch coincides on the palm with that found after complete division of the ulnar nerve. The whole palmar surface of the little finger and the greater part of the ulnar half of the ring finger are insensitive to cotton wool. On the dorsum of the hand, the loss of sensation may occupy the ulnar half of the two terminal phalanges of the ring, and the whole of the two terminal phalanges of the little finger ; or the whole little finger and a small portion of the ulnar border of the dorsal surface of the hand may be insensitive to light touch. But, wherever it may be situated in any individual case, the border separating the loss of sensation on the palm, from the normal area on the back of the hand, is an indefinite one. Previously, whenever loss of light touch has been under discussion, the borders of such loss have been spoken of as lines. That is to say, the passage, from a part over which cotton-wool is appreciated to one where it no longer produces any sensation, is so rapid, that for practical purposes it may be repre- sented by a line. This is not the case when the dorsal branch of the ulnar nerve has remained intact. The ulnar portion of the palm of the hand is

74 STUDIES IN NEUROLOGY

insensitive to cotton wool ; but, as the stimulus progresses towards the dorsal surface, the point at which it first evokes a sensation is uncertain, and the area of anesthesia seems to merge gradually into the complete sensibility of the back of the hand.

The extent to which sensation to prick and to the extremes of heat and cold is lost seems to vary greatly. It may be that the only absolute loss of sensation is found over the terminal two phalanges of the little finger on the palmar aspect, and over the terminal phalanx behind ; or the whole ulnar third of the palm, the whole palmar surface of the little finger and its two terminal phalanges on the dorsal surface may be entirely insensitive.

This absolute loss of sensation, however extensive it may be, merges gradu- ally into the area of partial loss and is not constant. Like all parts where sensation to prick and to the extremes of heat and cold is defective, the extent of the loss varies according to the temperature of the hand and the general condition of the patient. Thus in Case 24 (Table II., fig. 6, B, p. 73), the sensibility improved and again deteriorated, although the two ends of the divided nerve remained effectively separated.

In most cases, where the dorsal branch is intact, the considerable extent to which the borders of loss to light touch and to prick are separated from one another, renders it particularly easy to determine the character of sensation obtained from the intermediate zone. When pricked, the patient withdraws his hand with an exclamation, as soon as the area is reached where light touch is lost. Ice and water at 50° C. can be appreciated, water between about 22° and 40° cause a sensation of touch only. But, even though a prick can be perceived, it produces a widely diffused, tingling sensation, and two compass points are not distinguished, even when separated for a distance of 4 cm.

The dorsal branch seems to supply sensibility to light touch to the lower half of the ring finger on its ulnar aspect, and to the greater part of the ulnar third of the back of the hand. If it remains intact, there may be no loss of sensation to prick on the palm or first and second phalanges of the little finger after division of the ulnar nerve. Or the extent of the area supplied by the dorsal branch may be so small that all sensation is lost over the ulnar palm, and the analgesia occupies the two terminal phalanges of the little finger, and even laps slightly on to the dorsal surface of the hand.

Thus, it would seem that the part played by the two main branches of the ulnar nerve in supplying sensation of light touch to the hand varies little, but the border between the areas they supply, unlike any touch border yet described, is not fixed ; the parts, where sensation is lost to light touch, merge gradually into the back of the hand, where sensation is unaffected. But there is great individual variation in the extent to which sensation to prick and to the profounder degrees of heat and cold is lost. No two cases are exactly alike, and any focus of absolute analgesia that exists is surrounded by a wide area of partial loss to prick.

INJURY TO THE PERIPHERAL NERVES 75

§ 4. — DIVISION OF THE MEDIAN NERVE

Usually, when the median nerve is divided, the skin over the dorsal and palmar surfaces of the two terminal phalanges of the middle and index fingers becomes insensitive to light touch, pain and temperature. But cutaneous sensibility may also be lost over a wider area. The palmar aspect of the thumb, the hypothenar eminence and the greater part of the median half of the palm may be completely insensitive to prick. In such cases, the loss of all forms of cutaneous sensation nearly corresponds to the area assigned by anatomy to the supply of the median nerve. But so great a loss is not present in the majority of cases. The extent to which the palm and the palmar aspect of the thumb are affected varies greatly ; but on the dorsal surface of the index and middle fingers, the boundaries of the analgesia are remarkably constant, reaching as a rule to the folds of the skin over the first interphalangeal joint of both fingers.

The extent to which sensation to pain and to temperature is completely lost varies greatly and cannot be said to be exactly similar in any two cases. But the area over which light touch cannot be appreciated is more constant. Its borders usually extend from the radial edge of the thumbnail along the radial border of the thumb to the fold at the base of the thenar eminence ; thence it passes up the great central line of the palm to the cleft between the middle and ring fingers. It includes a variable portion of the radial half of the palmar surface of the ring finger and on the dorsal surface the radial third of the terminal two phalanges of the ring finger, and the skin over the terminal two and a half phalanges of the middle and index fingers. From the radial side of the index finger the border slopes towards the thumb, running along the extreme free edge of the first interosseous space, and thence extends up the thumb, to end at the ulnar border of the nail. The area, over which light touch is lost, corresponds on the palm almost exactly with that assigned by anatomy to the median nerve.

Although cotton wool is the best means of marking out this border, light touch is not the only form of sensation which there undergoes a change. Temperatures between about 22° C. and 40° C. are entirely unperceived as soon as this line is passed, and the painless interrupted current, generated with no iron in the circuit, ceases at this border to cause sensation, though well appreciated on the normal skin.

Thus, after division of the median nerve, exactly as with the ulnar nerve, an intermediate zone makes its appearance between the boundary for loss of light touch and the boundary of those parts over which sensation is absent to prick. Closer examination of this intermediate zone shows that sensation, produced by stimuli applied within it, has the same characteristics as that from the similar area, caused by division of the ulnar nerve. A prick usually causes pain more disagreeable in character than that of the normal skin. The patient has an urgent desire to withdraw his hand and cries out, or shows some obvious

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sign of discomfort. The sensation produced is widely diffused and badly localised; it is said to be a "numb, tingling pain." So characteristic may be this form of sensation, that the border at which light touch ceases to be perceived can be frequently marked out by dragging the point of a pin lightly across the skin from normal to abnormal parts, noting at what point the character of the sensation so produced undergoes a change.

Temperatures between about 22° C. and 40° C. are unperceived when applied within this area ; but the more extreme degrees of cold and of heat are usually well appreciated, although they cause a diffuse, badly localised, tingling sensation, unlike any effect produced upon the normal skin.

§ 5. — VARIATION IN THE EXTENT OF THE AREA SUPPLIED BY THE

MEDIAN NERVE

Among the twelve cases, where the median nerve proved at the operation to have been divided, there was but little variation in the extent of loss of sensa- tion to light touch and minor degrees of temperature. In all, the ring ringer was affected to a greater or less degree, usually one-half (six cases) or one-third (three cases) being anaesthetic ; but in two instances the anesthesia occupied a small portion only of its extreme radial aspect, and in one two -thirds of the whole finger. On the palm, the border may vary between a line drawn through the axis of the middle, and one drawn through the axis of the ring finger. The small variations which occur on the dorsal surface, in the extent to which the index and middle fingers are insensitive, can be best appreciated from the series of diagrams on fig. 7. The greatest variation occurs on the middle finger, where the anesthesia may extend over the two terminal phalanges or may occupy the whole finger to the base. Thus, the extent of the loss of sensation to light touch, and to minor degrees of temperature, is remarkably constant and varies within small limits.

These differences are trivial compared with the wide variations in the extent of the loss of sensation to prick, variations so profound that no two instances can be said to resemble one another exactly. In estimating the extent of this analgesia, it is important to use cases only in which the nerve was proved by operation to have been divided, and to choose only such observations as were made as soon as possible after the occurrence of the injury, before recovery could have begun.

Twelve of our cases come up to this standard. Among them five showed so large an amount of loss of sensation to prick, that the whole of the palm usually assigned to the median nerve, together with the palmar aspect of the thumb and both index and middle fingers, was analgesic. In fig. 7, L, the loss of sensation to prick on the palm was somewhat less extensive, but one- third of the ring finger was analgesic. In every case, the extent of this loss of sensation was different, until in fig. 7, A, it reached the smallest proportions we have yet seen. Here, scarcely the terminal two phalanges of the index

INJURY TO THE PERIPHERAL NERVES 77

FIG. 7.

To show the loss of sensation produced by division of the median nerve. The area of complete cutaneous insensibility is marked in black. The parts insensitive to light touch and to the intermediate degrees of temperature are enclosed within a line.

Most of these cases will be found on Table I., p. 90.

A represents the loss of sensation in Case 7; B, Case 11; C, Case 13; D, Case 6; E, Case 3; .F, Case 12; G, Case 8; H, Case 4; I, Case 9; J, Case 10; L, Case 5. K is taken from a woman who completely divided her median nerve in the neighbourhood of the elbow. We examined her on several occasions, but she disappeared before recovery of sensation began.

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and middle fingers were affected, and prick could be appreciated over the whole of the palm of the hand and over the palmar aspect of the thumb.

Thus, it is impossible to lay down any general rule, even with regard to the usual extent and distribution of loss of sensation to prick when the median nerve has been divided. We can only say, that, when it reached its wide extent, it almost corresponded to the area of loss of sensation to light touch, or, when the analgesia was reduced to its smallest proportions, scarcely the whole of the terminal two phalanges of the index and middle fingers were rendered insensitive to prick. Between these two extremes, every variety may occur.

It might be supposed that the presence of a considerable area of loss of sensation to prick on the palm depended upon injury to the descending branches of the external cutaneous nerve. But in the patient from whom fig. 7, K, was taken the nerve was divided by a wound in the fold of the elbow. Moreover, in fig. 7, L, the extent of the analgesia was larger than in any other instance that has come under our notice, and yet the nerve had been divided through a small punctured wound at the wrist, which could not have injured any considerable number of fibres of the external cutaneous.

§ 6. — DIVISION OF BOTH MEDIAN AND ULNAR NERVES

An extensive wound of the wrist may divide both the median and the ulnar nerves, causing paralysis of all the intrinsic muscles of the hand and widespread loss of sensation. To produce such great destruction the wound must be unusually severe, and, commonly, one or other nerve, though injured, escapes complete division. This is the condition in the majority of those cases where the median and ulnar nerves are supposed to have been divided. But amongst our patients were two in whom both nerves were seen to be cut across at the time of the original wound, and one, where they were divided seven weeks after the original injury for the purpose of secondary suture.

Taken in connection with a number of cases where both nerves were gravely injured, this material, though small, is sufficient to determine the extent to which light touch is affected when the two nerves are completely divided. But the loss of sensation to prick varied so greatly in the three instances of undoubted division, that it is impossible to say to what extent this form of sensation is most commonly lost.

Sensation to light touch is abolished by this injury over the whole palm and over the palmar aspect of the thumb and all the fingers. The outline of this area on the thumb corresponds, when uncomplicated by injury of other branches, to the similar border produced by division of the median nerve, and, like it, varies in the extent to which the thenar eminence is involved. Sometimes the ansesthesia over the proximal part of the base of the thumb is too extensive to be due entirely to destruction of the median nerve, and is probably caused by division of fibres from the external cutaneous descending

79

on to the palm. Any cut, running across the wrist from side to side completely, must tend to divide these branches.

On the posterior surface, the border of the area over which light touch and minor degrees of temperature are lost varies, according to whether the dorsal branch of the ulnar nerve has been severed or not. In the three cases of complete division of both main trunks, the ulnar nerve had been divided above the point at which this branch was given off. The loss of sensation on the back of the hand, therefore, corresponded to that seen after complete division of the ulnar nerve. On the dorsal surface of the index and middle fingers, the anaesthesia extended to the proximal fold over the first interphalangeal joint in two cases, and to a point half-way between this fold and the knuckle in the third. On the thumb, the border ran from the ulnar aspect of the base

To show the loss of sensation produced by complete division of both median and ulnar nerves. The area of complete cutaneous insensibility is marked in black. The parts insensitive to light touch and to the intermediate degrees of temperature are enclosed within a line.

These cases will be found on Table III., p. 96.

A shows the loss of sensation in Case 26, B in Case 28, and C in Case 25.

of the nail to the dorsal aspect of the free edge of the first interosseous space. Thence it passed up the radial aspect of the base of the index to join the line on the dorsum of this finger.

The extent to which light touch and the minor degrees of temperature were lost corresponded exactly to the loss of sensation produced by division of the ulnar nerve, added to that caused by division of the median. Occasionally, the loss on the palmar aspect of the thumb was a little increased by destruction of branches of the external cutaneous running downwards over the wrist.

To prick, the loss of sensation varied so greatly that an attempt to describe in detail its boundaries in each case would be wearisome, and the reader is referred to fig. 8. The greatest loss appeared in Case 25 (fig. 8, c), where the whole palm and palmar aspect of the thumb were insensitive to prick. But it must be remembered that, in this patient, all the structures on the front of

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the wrist had been divided to the bone, and amongst them must have been included the descending branches of the external cutaneous nerve. In both the other cases, loss of sensation to prick was less extensive on the palm (fig. 8), and they probably belonged to the group in which the median nerve supplies exclusively the fingers only.

On the dorsal surface, the index, middle and ring fingers were insensitive from the tip to the lowest fold over the first interphalangeal joint in two of the cases ; in one, the dorsum of the index seemed to be sensitive to prick. In all, the whole of the little finger and a varying portion of the ulnar aspect of the dorsum of the hand were analgesic. The material at our disposal is small ; but it would seem that division of the median and ulnar nerves tends to produce the following results :—

(1) Sensation to light touch is lost over the whole of the palm. Loss of sensation on the back of the fingers extends at least to the first interphalangeal joint ; and if the ulnar nerve has been divided above its dorsal branch, the anaesthesia invades the whole of the ulnar half of the middle finger, the whole little finger, and a variable extent of the dorsal surface of the hand.

(2) The loss of sensation to prick varies greatly in extent. In one instance, the whole palm was insensitive to prick. In the remainder, the thenar eminence and the extreme radial portion of the hand were sensitive to