The physiology and pathology of the cerebral circulation; an experimental research

Preface

In the following pages will be found the substance of three Lectures which I delivered as Hunterian Professor at the Royal College of Surgeons in February last.

I have largely been enabled to carry out the researches of the past five years therein detailed, through the munificence of the Worshipful Company of Grocers. This volume contains a report of the work done by me as their Research Scholar. In writinof some of the sections of this work I have drawn on papers previously published by me in the Proceedings of the Royal Society, the Journal of Physiology, and the British Medical Journal ; other sections, such as those on the Cerebral Pulsation, the Cerebro-sj)inal Fluid, Cerebral Anaemia, and Cerebral Compression are new, and contain an account of experiments hitherto unpublished.

I have been partly supplied with the means of research by grants from the Royal Society Government Grant, and the British Medical Association ; and I owe a debt of gratitude to Professor Burdon Sanderson, Professor Schiifer and the Authorities of the London Hospital Medical College, whose laboratories and laboratory appliances have been placed at my disposal.

vi PREFACE.

I have gained very greatly from the criticisms of my friends, Professor Burdon Sanderson, Professor Schafer, Dr. Rose Bradford, Mr. B. Moore, Dr. Arthur Keith, Dr. J. H. Sequeira, Mr. Harold Barnard, Mr. C. Wall and many Members of the Physiological Society, who have at different times watched my experiments and corroborated my results.

I am deeply indebted to Mr. Bayliss and Mr. Nabarro, who have been my co-workers in part of these researches.

Mr. Langley has been generous enough to lend me, from the Journal of Physiology, Figures 5, 6, 7, 8, 11, 13, 14, 15, 16, 17, 18, 19, 20, 21 ; for Figures 35, 36, 37 I am indebted to the publishers of Morris's " Anatomy." To all these friends I tender my warmest thanks.

LEONARD HILL.

Mmj 22, 1896.

Contents

Introduction :

Origin and Plan of Research .....

Section I.— PULSATIONS OF THE BRAIN. Method of Research — New Instruments

Cerebral Pressure Gau.ge .......

Pulsation of Cerebro-spinal Fluid ......

The Brain Pulsates in the Closed Cranium

Pulsation of Cerebral Veins ......

Cerebral Venous Circulation — Method of Investigation Resemblance of the Cranial Cavity to an Oncometei- Fallacies of the Oncometric Method .....

Absence of Valves in the Cerebral Veins . . . .

Pathological Changes in the Cerebral Pulsation Summary of Section I. .

Section II.— THE CEREBRO-SPINAL FLUID. 9 10 10 10 11 12 12 13 13 15

Anatomy of the Subdural and Subarachnoid Spaces . . .16

Experiments on the Injection of Fluid into the Cranio-

VERTEBRAL CaVITY . . . . . . . .18

Method of Research . . . . . . . .19

Irrigation of the whole Cranio- vertebiul Cavity . . .19

Filtration of Fluid from the Cranial Cavity . . . .20

The Pressure at which Filtration takes place . . . .20

Filtration through the Dura Mater 20

A Typical Experiment on the Filtration of Fluid . . .21 viii CONTENTS.

PAGE

The Pathways of Filtration . . . . . . .22

The Secretion and Absorption of Cerebro-spinal Fluid . 23

Amount of Cerebro-spinal Fluid . . . . . .24

Subarachnoid Space a Potential but not Actual Space . .25 Transudation of Cerebro-spinal Fluid, its Dependence on Cerebral

Venous Pressure . . . . . . . .27

Summary of Section II. . . . . . . . .28

Section III.— THE CEREBRAL CIRCULATION. The Monro-Kellie Doctrine

History . . . .

Fallacies of Post-mortem Examination

The Monro-Kellie Doctrine tested by Experiment

History of Previous Experiments

Method of Research .....

History of Previous Methods op Investigating the Cerebral

Circulation ......... 37

Method of Research 40

Search for Cerebral Vaso-motor Nerves . . . .42

Method of Experiment - . . .42

Stimulation of Vago-sympathetic Nerves . . . .43

Stimulation of Dorsal Spinal Cord . . . . . .43

Stimulation of Stellate Ganglion . . . . . .45

Histological Seai'ch for Cerebral Vaso-motor Nerves . .45

Previous Researches into Cerebi-al Vaso-motor Nerves . . 45

Negative Results . . . . . . . . .46

Effect op Drawing a Ligature round the Neck . . .46 Stimulation of the Peripheral End of the Vagus Nerve . 46 Discussion of some Physical Conditions of the Cerebral Circulation .......... 46

Direct Continuity of the Cerebral Veins with the Thoracic

Veins 49

Absence of Valves ......... 49

Cerebral Venous Pressure varies absolutely as Pressure in

the Vense Cavte ........ 50

Intracranial Pressure is the same as Cerebral Venous Pressui-e . 50 Intracranial and Cerebral Venous Pressure vary directly but not

absolutely as Arterial Pressure . . ... . .50

30 31 33 35 35 36

CONTENTS.

IX

Workei-s

Excitation of Vagus the Cerebi'al Circula-

Cerebro-spinal Fluid Pi'essure fails to vary absolutely as

Inti'iici-aiiial Pressui-e A Typical Experiment Confirmation of Experiments l)y Previous The Cerebral Vessels as Kigid Tubes Effect of Blocking Cerebral Veins during Discussion of Previous Results Excitation of Sensory Nerves, Effect on

tion Influence of Anesthetics

Chloroform

Ether

Moi'phia .

Injection of Curari Injection op Amyl Nitrite Discussion of Previous Results Injection of Acids and Alkalies Injection of Brain Extracts Epileptic Fits Injection op Absinthe .

Injection of Strychnine Injection op Supra-renal Extract Effect of Ice applied to the Head and Abdomen . Principles of the Cerebral Circulation . .• . . The Cerebral Blood Volume almost an Invariable Quantity A Rise of Arteiial Pressiire increases the Cerebral Blood Flow Fallacy of the Conti-aiy Doctiine ......

Schema of Cerebi'al Circulation ......

Intracranial Tension ........

Past Methods of Investigation ......

Intracranial and Cerebral Venous Pi-essui-es ....

Range of Vaiiation .........

Mechanism of Regulation of the Cerebral Circulation Cerebral Congestion ........

Summary op Section III. .......

50 50 51 51 52 54

55 57

CONTENTS.

Section IY.— INFLUENCE OF THE FORCE OF GRAYITY ON THE CIRCULATION OF THE BLOOD.

PAGE

Method op Reseaech . . . . . . . .81

Estimation of Intracranial Tension in Man . . . .81

Hydrostatic and Dynamic Moments . . . . .83

Normal Effect on the Carotid Artery . . . . .84

on the Respiration . . . . . . . .85

on the Femoral Artery . . . . . . .85

Effect on the Intracranial Tension . . . . . .86

Compensation of the Hydrostatic Moment by the Dynamic

In the Monkey ......... 87

Effect on the Venous Circulation . . . . .88

on the Cerebral Yenous Circulation . . . . .90

Influence of Anaesthetics . . . . . . .93

Ether 95

Effect of Yaso-motor Paralysis . .... . .98

Section of Dorsal Cord . . . . . . . .98

of Splanchnic Nerves . . . . . . .98

Effect of Curari and Amyl Nitrite 98

Effect on the Respiration . . . . . . .98

Effect of Bandaging the Abdomen . . .■ . .99

Excitation of Divided Spinal Cord . . . . . .102

of Splanchnic Nerves . . . . . . .102

Influence of Asphyxia ........ 102

of Bandaging the Abdomen during Asphyxia . . ,102

Influence of Injecting Supra-renal Extract . . .102 Discussion of Experimental Results . . . . .102

Syncope . 103

The Arteriometer . . . . . . . . .105

Compensation for Gravity, the Clinical Key to the Yaso-motor

Shock 106

Methods of Rapidly abolishing the Compensation for Gravity . 107 Cheyne Stokes and Traube-Hering Curves . . . .108

CONTENTS. xi

PAGE

Influence OF Position AFTER Severe H^EMOiauiAGE . .108

Injection of Nonnal Saline after HtBmoiThage . . . .108

Danger of Administering Chloroform in the Vertical

Refutation of the Conclusions of the Hyderabad Gominission . 101) Causes of Death from Chloi/oforni . . . . . .110

Methods of Relieving Chloroform Collai3se . . . .110

Influence of Opening the Skull on the Cerebral Circulation Ill

Influence of Position in Heart and Lung Disease . .111 Abdominal Belts . . . . .111

Loss of Memory in the Vertical Position . . . .112

Rabelaisian Effects of Fear . . . . . .112

Summary of Section IV. 113

Section V.— CEREBRAL AN^^MIA. Methods of Investigation . . . . . .117

Ligature of the Four Cerebral Arteries . . . .122

in Rabbits 122

Symptoms of Acute Cerebral An.^mia . . . . .125

Causes of Death ......... 125

Pressor Effect of Closing the Four Cerebral Arteries . .130

Depressor Effect of Re-opening One Carotid . . . .130

Unstable Condition of Bulbar Centres aftei- Ligatui-e of the

Cheyne Stokes and Traube-Hering Curves .... 130

Dependence of Respiration on Blood Pressure . . . .132

Cheyne Stokes Respiration in Hybernating Animals . .133

Production of Cerebral Anemia by Forcible Injection into

One Carotid Artery . . . . . . .135

Remote Effect of Ligature of the Four Cerebral Arteries

Symptoms of Idiocy . . . . . . . . l;-37

Diary of the Animal's Condition . . . . . .137 xii CONTENTS.

PAGE

Recovery of the Animal . . . • • • • .139

Post-mortem Injection of the Circulation after Ligature of the

Four Cerebral Arteries Pathways of Anastomosis Effect on the Petinal Circulation Remote Effects in the Monkey Cerebral Anjemia m Man

Compression of Common Carotids in Man

Cortical Spasm Produced thereby

Ligature of the Carotid Arteries in Man Epilepsy ......

145 145 146 146

Refutation of the Cerebral Vaso-motor Spasm Theory . 145

Bulbar Spasms ....

Cortical Spasms ....

Theory of Epilepsy ....

Sleep .......

Cerebral An?emia and Venous Congestion in Sleep . . 147

Yaso-motor Centre, the Hub round which Turns the

Wheel of Active Mental Life 148

Theory of Sleep ■ • .148

Summary op Section V. 149

Section VI.— METABOLISM OF THE BRAIN

Production of Heat in the Brain . . . . ■ . .152

Fallacies of Previous Investigations . . . . .152

Determination of the Exchange of Blood-Gases in Brain and

Muscle 154

The Brain not a Seat of Active Combustion . . . .155

Section VIL— CEREBRAL COMPRESSION.

Symptoms of Apoplexy . . . . . . . .160

Discussion of Past Researches . . . . . . .162

Method of Investigation . . . . . . . .164

Compression by Continuous Injection of Fluid at a Constant Pressure . . . . . . . .165

Discussion of Results . . . .. . . .168

Escape of Injection Fluid . . . . . . .168

CONTENTS. xiii

PAGE

Translocation of , the Brain and Blockino; of tlio Istlnnus

Tentorii Oei-ebelli and Foramen Mai^nnm . . . 1G9

Production of H.-emorrhage in the Cranial Cavity . . 175 Non-absorption of Blood-clot . . . . . .175

Effect on Intracranial Tension and Cerebral Venous Pressure . ] 78 Symptoms of Apoplexy, produced by Cerebral Anfemia . .180

Effect on Bulbar Centres of Local Haemorrhage . . .181

Compression by a Foreign Body of Limited Volume . .181 Pressure Discontinuity between the Chambei\s of the Cranio-

vertebral Cavity . . . . . . . .182

Pressure not Equally Transmitted by Bi-ain in all Directions . 182 Major Symptons of Apoplexy produced by Compression of

Bulbar Centres Symptoms op Compression

Epileptic Fits Inhibition of Heart Spasm of Eespiration

182 184 184 185 185

Pressor Effect 186

Causes of Death from Compression . . . . .187 Traube-Hering and Cheyne Stokes Curves . . . .187

Remote Effects of Intracranial HiEMORRHAGE . . .188 Congestive (Edema . . . . . . . . .189

The Circulus Vitiosus 189

Inflammatory Qildema . . . . . . . .189

Circulus Vitiosus established by a Rise in Arterial Tension . 191 Depletion as a Form of Treatment . . . . . .193

Tumours of Brain ......... 194

Mechanism by which Compression is Produced . . .196

Tumour and Cerebral Oedema . . . . . .197

Meningitis and Cerebral Abscess . . . . . .197

Meningocele 198

Serous Apoplexy, Fallacy of . . . . . .199

Summary of Section VII. . . . . . .199

Index of Names ......... 207

LIST OF ILLUSTRATIONS.

J^'"- PAGE

1. A. Brain- Pressure Gauge .......;»

B. Instrument for producing Local Compression of the Brain '.)

2. Section of Dog's Cranium showing Torcular Herophili 1 1

3. Key and Retzius' Injection of Subarachnoid Space . . 25

4. Methods of Investigating Cerebral Circulation . . .41

5. Excitation of Central End of Upper Dorsal Spinal Cord . 44

6. Effect of Drawing a Ligature round the Neck . . .47

7. Excitation of Pei-ipheral End of Vagus . . . .48

8. Excitation of Peripheral End of Vagus; Cerebral Venous

Exits partly blocked 52

9. Effect of Asphyxia 56

10. Influence of Amyl Nitrite . . . . . .60

11. Epileptic Fit produced by Absinthe . . . .65

12. Schema of Cerebral Circulation ...... 69

13. Instrument for Investigating Intracranial Tension in Man 82

14. Effect of Gravity, Carotid Artery 84

15. Effect of Gravity, Femoral Artery 85

16. Effect of Gravity, Carotid Artery and Intracranial Tension 86

17. Compensation for Hydrostatic Effect of Gravity in Monkey 87

18. Effect of Gravity on the Cerebral Venous Circulation . 90

19. Influence of Chloroform on Gravity Effect . . . .92

20. Influence of Chloroform on Gravity Effect . . . .94

21. Influence of Ether on Gravity Effect . . . .96

22. Effect of Gravity after Section of Upper Dorsal Spinal Cord 98

23. Influence of Bandaging Abdomen . . . . .99

24. Influence of Bandaging Abdomen . . .100

25. Ligature of Four Cerebral Arteries in Rabbit . . .122 2 0. Ligatvire of Fom- Cerebral Arteries in Cat, Cheyne Stokes

Respiration . . . . . . .126 xvi LIST OF ILLUSTRATIONS.

FIG. PAGE

27. Ligature of Four Cerebral Arteries in Cat, Primary Vaso-

motor Paralysis . . . . . . .127

28. Ligature of Four Cerebral Artei-ies in Oat, Primary Re-

spiratory Failure . . . . . . .128

29. Pressor Effect of Closing Foiir Cerebral Arteries — Depressor

Effect of Opening One Artery . . . • .129

30. Instability of Bulbar Centres after Closure of Four Cerebral

31. Cheyne Stokes Respiration and a Plethysmographic Record

of Arm in Man 134

32. Optic Disc of Dog with Four Cerebral Arteries Ligatured . 140

33. Methods of Producing Cerebral Compression . . .156

34. Compression by Injection of Fluid into Cranial Cavity . 168

35. Section of Cranium ........ 170

36. Section of Cranium . . . . . . . .171

37. Section of Cranium . . . . . . . .172

38. Compression by Haemorrhage into Cranial Cavity . .178

39. Effect of Compression on Cerebral "Venous Pressure . .179

40. Local Compression — Vagus Inhibition . . . .185

41. Local Compression — Pressor Effect . . . . .186

THE CEREBRAL CIRCULATION.

Introduction

^ The study of the exact attributes of the cerebral circulation, and how and why, from interference with the physical conditions of the normal cranio -vertebral contents, pathological states may arise, is one of the most difficult and at the same time one of the most interesting questions with which a physiologist can grapple. The hydrodynamical conditions of the cranium are so complex, and the methods of research surrounded, as they are, with many difficulties, are so exceedingly liable to lead to error, that a man's wits must indeed be about him that he may walk straight through so tangled a pathway. The whole difficulty of the subject depends upon that shell of rigid bone, a shell inexpansile, unyielding to atmospheric pressure, enclosing a brain of which the nervous substance is utterly incompressible. From the outer world of the body into the base of the cranial cavity pass pulsating arteries. These arteries permeate that membranous capsule of the brain, the pia mater, dip into the nervous matter and end in an all-pervading capillary meshwork. Between the various arteries coursing over the surface of the pia mater there is free communication ; by injection into one tributary the entire arterial system can be here readily filled. The injection at first passes rapidly through the main stems, and it is only when these have become distended that the meshwork in the pia begins to fill. From this capillary meshwork, fine branches run into the brain substance, and thence arise veins, which, trending towards the roof of the cranium, there pass into the large venous sinuses, emissaries of which once more gain the outer world. The brain and the blood which circulates through it fill the cranial cavity almost entirely. In the space that remains is the cerebro-spinal fiuid, a fluid of peculiar constitution which moistens the surface of the brain. In the vertebral canal, where it bathes the spinal cord, it is relatively more in amount. The nervous substance of the brain is incompressible as water : Grashey has experimentally determined this point : the living brain full of blood is as expressible as a sponge.

The research on which I have been continuously engaged for the last four years was suggested to me by Professor Burdon Sanderson, and the fruits of this research, such as they are, which I shall endeavour to lay before you in these lectures, owe their origin primarily to him who planted the seed, whether in fruitful or unfruitful soil time and trial will tell.

It is so easy by incomplete and faulty experiment and hasty generalisation to throw discord into the

INTRODUCTION". 3

accepted pathology of the clijiician, that the experimental method has often and most deservedly been met by hun with incredulity and passed over with neglect. That the experimental method is a true standard by which cliiiical })athology can be measured goes without saying. It is the complete carrying out of the method that alone fails. Such a subject as the hydrodynamics of the cranium can only be investigated by experiment. By exjDeriment the theory of the clinician and the conclusions of the morbid anatomist can be tested and the hand of the surgeon guided. It is as fatal to depend on results gained from the dead animal or from the use of artificial schemata, as to discuss the physics of this question without appeal to experiment at all. In the hands of many workers this method has led to fallacy, since they failed to realise that the physical conditions of the cranial cavity and of the circulation are not wholly known, and therefore no scheme or model can adequately represent them. Experiment on the living animal solely can throw light on these complex questions, and schemata are of value in so far only as they illustrate the facts gained by experiment.

The method of working I have followed has been experimental. I have worked out each step in research and have then, and only then, appealed to the evidence of the literature of the subject. In this way I have found that many of my results had been forestalled by former workers. Although such a method may lead to some personal disappointment, yet I believe it to be of the greatest value, because every one of the conelusions which I have finally reached is corroborated by my own independent and unbiassed experiment. If I have failed anywhere in acknowledging the work of others, it is from ignorance and not by intention.

Section I. The Pulsations Of The Brain

Observations on the movements of the brain are to be found recorded in the earhest medical writings. Galen and his followers thought that by the diastole of the brain, the wevina, the spirit of life was sucked in through the cribriform plate and mingled with the vital spirit which ascended by the arteries from the heart. For, in the words of a Galenist, " the heart, the fountain of life, doth boil up out of the finest parcel of blood, a little flame called a vital spirit, and it panteth by reason of its heat incessantly." In the laboratory of the cerebral ventricles the animal spirits were prepared from this mixture and driven by the systole of the brain into the nerves. " There the animal spirit doth work local motion whilst running up and down through the nerves and filling the muscles ; it on this side stretcheth tendon, on that side it j^uUs them back. But being weary it seeks rest, and therefore, having left the organs of sense, hideth itself into its retirements, which thing we call sleep ; it refresheth itself in the brain, and running up and down its cells, upon what vain visions it light reassumes them to be viewed over which we call a dream." The waste pro-

6 THE CEKEBRAL CIRCULATION.

ducts from the preparation of these animal spirits were, it was thought, excreted by the nose and the infundibulum. Apoplexy was attributed to the stoppage of this excretion. Such was the doctrine held by some of the Galenists.

It was supposed by others, that the dura pulsated, and, by driving onward the animal spirits, produced movements of the soul and of the muscles. Thus Baglivius and Pacchionus thought that the dura mater was a muscular and contractile membrane, whilst Willis and Mayow discovered, what they held to be, the contractile fibres of this membrane. In ascribing the movements to the pulsation of the arteries in the dura, Fallopius came nearer to the truth ; Kidley, a clearheaded anatomist of the seventeenth century, ascribed the pulsation entirely to the cerebral arteries. De la Mure, Haller and Lorry, by finally establishing the cardiac and respiratory origin of the cerebral jDulsation, proved that the dura possessed no independent power of movement in itself, and showed that the collapse of the chest-wall pressed" upon the thoracic veins, and drove back the venous blood, thus causing the expiratory expansion of the brain.

In recent times Donders, denying that any movements of the brain could take place in a closed skull, opened up a fresh phase of discussion and inquiry. He trephined an animal and observed a pulsation in the vessels of the pia. He then fixed into the hole a glass window, and found that all sign of pulsation ceased. Experimenting on the same lines, Leyden also denied to the brain any movement in the closed skull. Longet went still further, and denied that even the cerebral arteries could pulsate. The reason given for this strange assertion was that the brain completely filled the rigid unyielding box of the skull in which it lay enclosed. Schultz, however, by employing a better light to illuminate the cranial window, was able to discern and bear witness to the pulsations of the vessels in the closed skull. In the last twenty years the cardiac and respiratory movements of the brain have been observed and recorded by Ley den, Jolly, Salathe, Franck, Oudin, Mosso and many others. Records have been taken from animals, from men with cranial defects, from infants by means of the fontanel. With a tambour, Bergmann recorded the movements in the brain of a woman whose skull was defective. On compressing both carotids the pulsation ceased. The cardiac expansion of the brain was synchronous with the systole of the heart, the resj)iratory expansion with expiration. Salathe recorded simultaneously the cerebral movements, the respiration, and the blood pressure in the carotid. Franck observed a great expansion of the brain on forced expiration, and noted that the cerebral movements were comparable to those perceived in a limb enclosed in a plethysmograph.

Duret was the first experimenter to record the pulsations of the cerebro-spinal fluid within the closed cranio-vertebral cavity. This he did by means of a tambour placed in apposition to the occipito-atlantal ligament. Bonders and Berlin thought that when the cranial cavity was closed in proportion to the expansion of cerebral arteries the cerebral veins collapsed, and on each diastole of the arteries cerebro-spinal fluid was absorbed, to be once more transuded on systole. In these two ways space was made for the cardiac systolic increase of the arteries, and the brain mass did not as a whole either expand or contract. Bergmann pointed out that in the cardiac systolic phase the capillary pressure is at its highest, and therefore transudation rather than absorption would occur. Althan showed that the errors of Donders and Berlin arose from neglect of the fact that the brain pulsates in a direction where resistance is least. Thus when the cranium is trephined and the dura opened, the pulse can scarcely be seen in the occipito-atlantal membrane, for the trephine hole has now become the seat of least resistance. Similarly, when a trephine hole is closed by a glass window, the occipito-atlantal membrane becomes the seat of least resistance, and a pulsation appears there. Franck very neatly exhibited this phenomenon by recording the pulsations of a limb placed in a plethysmograph. He fixed two tubes into the chamber of the instrument, and stretched across one of these tubes a diaphragm of thin india-rubber. The pulsations of the limb could now be seen in the open tube only, but if this were closed the elastic membrane in the other tube immediately responded to the movement.

I will now turn to my own method of demonstrating the movement of the brain in the closed cranium. I trephine a skull in the parietal region, worm the trephine hole with a mechanic's tap, carefully divide the dura without causing any haemorrhage, and screw a piece of steel tubing into the hole. Over the end of a piece of brass tubing of smaller diameter than the steel tube, but of equal length, I tie a piece of the thinnest india-rubber membrane (Fig. 1, a). This second tube is passed into the steel tube, and the two are screwed together by means of a male and female screw. By means of this mechanism the india-rubber membrane comes into exact apposition with the brain. Attached to the end of the brass tube is a piece of Sflass tubing; of a fine bore. This is connected with a

Fig. 1.

T-piece, one branch of which leads to a pressure bottle, and another to a mercury manometer. The whole apparatus is completely filled with water, and a bubble of air, to act as an index, is introduced within the finebore glass tubing. Before the apparatus is screwed into the steel tube the normal no-pressure position of the air index, when the tube is held horizontally and the membrane is flat, is marked on the glass tube. On screwing in the apparatus the air index, which is at first forced out, is again, by raising the pressure bottle, brought to the normal position. That is to say, the

10 THE CERBERAL CIRCULATION.

brain, which is shghtly bulged outwards by the intracranial pressure, is forced into that flattened position which it naturally must assume against the closed cranial wall. The elevation of the manometer by this method gives me the normal intracranial tension. The pressure of the cranial contents against the skull wall is exactly balanced, and the skull becomes once more a closed cavity. The air index in the cerebral pressure gauge — as I shall call this instrument: — perfectly exhibits cardiac and respiratory undulations of intracranial pressure. Now very frequently on opening the dura there is scarcely a drop of fluid to be seen between this membrane and the pia mater. The brain, therefore, is in close apposition to the dura, and we may rest assured that the brain itself pulsates in the closed cranium. This diastole and systole of the brain are made possible in the unyielding box of the cranium in two ways.

(1) By the ebb and flow of the cerebro-spinal fluid. The occipito-atlantal and other vertebral ligaments extend in cerebral diastole and allow the fluid to escape from the • cranial cavity, while in systole, through the elasticity of these ligaments coming into play, it is driven back. To what extent this can take place I shall show in the next section.

(2) By compression of the cerebral veins in diastole another mechanism is provided. Cramer was the earliest recorder of the cerebral venous pressure. He placed a cannula in a branch passing from the transverse sinus into the jugular vein, and noted a transmission of the pulse into this vein. Oaertner and

Wagner reached the same result })j ohservations' of the blood-flow from the same vehi. Tliis uietliod of obtaining cerebral venous pressure is exceedingly inconvenient, and entails large dissections in large animals, and even in such failure is frequent owing to clotting. The method which I have used to investigate the cerebral venous circulation is as follows. In

Fig. 2.

a dog the superior longitudinal sinus with its tributaries opens into a large venous cavity within the occipital protuberance. This bony cavity is the torcular Herophili. The transverse sinuses lie within the osseous part of the tentorium cerebelli and lead out of this cavity. Part of the blood finds its exit by the post-glenoid foramen and reaches the external jugular vein, but a large portion passes into the large sinuses which run down the vertebral canal. It is quite simple to drill a hole into the torcular, and then immediately to screw into the hole a brass tube filled with magnesium sulphate solution. This brass tube is connected with a water manometer. In Fig. 2 is shown a photograph taken from a longitudinal section of a dog's head immediately after death. A hole drilled into the torcular is marked out white in the figure. The manometer can be directly observed, or connected with a delicate tambour to record the movements. In this way a continuous record of cerebral venous pressure can be obtained with little dissection and considerable ease in dogs of small size. The manometer exhibits all the cardiac and respiratory pulsations, the latter in a very marked way. The brain is an organ which pulsates with every stroke of the heart and with every respiratory movement, and owing to its peculiar conditions, enclosed as it is in an unyielding box, the cardiac pulse is not entirely spent in distending the arterioles and capillaries, but is transmitted to the venous sinuses. The brain, as is shown by the cerebral pressure gauge, is lifted up by the stroke of the arteries at its base, and is thrown against the cerebral veins. By the rise of pressure in the right side of the heart, the blood in expiration is dammed back into the sinuses, and the brain must then expand more at the expense of the cerebro-spinal fluid. We find the contrary to occur in inspiration, the veins are emptied by the suction action of the thorax, the brain collapses, and the cerebro-spinal fluid reenters the cranial cavity.