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ON THE CIRCULATION OF THE BRAIN.

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vestigation, and the accumulation of facts have placed at our disposal. Still, it required some courage on the part of Dr. Burrows to announce to the assembled sages and seniors of his college that the principles upon which their practice in an important class of maladies is founded are erroneous, and to inculcate the absolute necessity of adopting measures of investigation to the use of which several of them are incompetent; but in his lectures there is an absence of self-sufficiency, a deferential mention even of the authorities he feels called upon to differ with, and an earnestness of tone in what he advances, that preserve him from the imputation of being a mere innovator, and enforce his claims to attention. Disciplined under the auspices of one of the best clinical teachers this metropolis has ever possessed, and furnished with the wide field of observation a large hospital alone can give, he has advanced no opinion without mature consideration and examination, and has advised no departure from routine practice without furnishing ample evidence of its inefficiency or its hurtfulness.

The work is divided into two portions. In the first of these, the erroneous doctrines respecting the cerebral circulation which have been commonly entertained are examined and refuted. In the second, the frequent dependance of functional and structural cerebral affections upon a diseased condition of the heart or its membrane is set forth.

I. On the Circulation of the Brain.-The opinion that the brain under all circumstances of health and disease contains absolutely the same quantity of blood, seems so contrary to common sense and daily experience, that its disproval would seem scarcely to require the careful elaboration Dr. Burrows has bestowed upon it; but when we consider it has been and is entertained by men of the highest eminence in the profession, when names such as Monro, Abercrombie, and Clutterbuck can be cited in its favour, it is evident that something beyond a mere negation of its correctness is called for. Its defence is based upon the mechanical structure of the cranium, and experiments upon animals. The cranium, it has been said, is a perfect sphere, the contents of which are protected from the effects of atmospheric pressure. Allowing that the bony case prevents that direct effect of pressure upon its soft contents which some other portions of the body are exposed to, the indirect effect exerted upon the blood entering at the orifices of the base is no less obvious.

In regard to the experiments upon animals, those which were performed by Dr. Kellie, and recorded in the first volume of the Medico-Chir. Trans. of Edin., have been quoted, first by Abercrombie, and subsequently by various other writers. The following are Dr. Kellie's propositions:

"1. That a state of bloodlessness is not discovered in the brains of animals which have died by hæmorrhage; but, on the contrary, very commonly a state of venous cerebral congestion. 2. That the quantity of blood in the cerebral vessels is not affected by gravitation, or posture of the head. 3. That congestion of the cerebral vessels is not found in those instances where it might be most expected; as in persons who die by hanging, strangulation, suffocation, &c. 4. That if there be repletion or depletion of one set of vessels (arteries or veins) in the cranium, there will be an opposite condition of the other set of vessels."

Dr. Burrows submits these experiments of Dr. Kellie to a renewed

examination, and is naturally surprised at finding that, in contradiction to the first proposition, instances of a sheep and dog are given, whose brains, after they were bled to death, contained considerably less quantity of blood than did that of a dog who was killed by tying the jugulars and carotids. In the face of such a contradiction Dr. Burrows saw no other resource than the institution of new experiments. He killed two rabbits, the one by opening the blood-vessels of the throat, and the other by strangulation. On examining the brains of each, 24 hours after, he found that of the former completely blanched, and that of the other as completely congested. Plates representing these conditions are appended to the volume. "In fairness to Dr. Kellie I should state, that I have attended at the slaughtering of sheep by butchers, and find the brains of those animals much less depleted than the brains of rabbits which have died of hæmorrhage. But the sheep did not die of simple loss of blood; but partly from the division of the pneumo-gastric nerves and cervical portion of the cord. These lesions, no doubt, influenced the appearances." The experiments which Dr. Burrows has made in reference to the influence of posture are also in contradiction with the conclusions of Dr. Kellie; for animals placed under the same circumstances after death, excepting the dependent condition of the head, presented very different appearances of the brain as regards congestion.

"It may now be asserted that the encephalon is not exempted from the law in physics-the gravitation of the fluids to the lowest part of the corpse. The discovery of the operation of this force on the blood within the cranium after death, suggests a precaution very essential to be followed, when it is desired to ascertain the precise amount of congestion of the cerebral vessels at the time of death. In such cases, a ligature should be placed around the throat, and drawn sufficiently tight to compress the cervical vessels, and arrest all flow of blood through them. This precaution will be most required in the examination of bodies, where, from the kind of death, the blood may be suspected to remain fluid in the heart and great vessels. The depending or elevated position of the head during the examination of the body, will not then induce deceptive appearances, which mislead us in our conclusions as to the previous amount of congestion in the cerebral vessels." P. 21.

To support this third proposition, Dr. Kellie adduces some instances of the brains of persons who had been hung presenting no remarkable congestion. Dr. Burrows, although maintaining that congestion of the cerebral vessels is generally produced by this or any other description of death which kills by obstructing respiration, admits that such congestion is occasionally absent. He attributes this to the rope having imperfectly compressed the external jugular on one side, and still more to the subsidence of the fluid blood during the subsequent suspension of the body, through the unobstructed cervical vessels, as also through the vertebral sinuses and spinal veins. In examining the bodies too, of those who have died from stran. gulation, the neck is usually cut across, and the thoracic organs inspected prior to the brain, the blood from which last thus becomes discharged through the divided cervical vessels.

Dr. Kellie's fourth proposition is founded upon the assumption that, the amount of blood contained within the cranium is always the same. This, we have seen, Dr. Burrows denies; and therefore does not admit the necessity of the adjustment of the equilibrium between the two classes of

1846.] ON VASCULAR PRESSURE WITHIN THE CRANIUM.

37

vessels. He believes, indeed, that the amount of extra-vascular serum in the cranium is very variable, depending upon the amount of blood in the arteries or veins being more or less than normal.

On Vascular Pressure within the Cranium, and its Influence on the Functions of the Brain.-Dr. Abercrombie denied the existence of such pressure-1, because "the cerebral substance is composed of inelastic fluids which are incompressible;" and 2, "because the brain is incompressible by any such force as can be conveyed to it from the heart through the carotid and vertebral arteries." In reply to the first of these, Dr. Burrows observes that the brain, although very incompressible, is highly elastic. The existence of an outward pressure produced by the passage of the blood into the vessels is seen when a portion of the cranium has been destroyed by accident or disease. Movements of the brain, dependent upon the arterial pulse and upon the respiration, have long been observed and commented upon under these circumstances. Whatever diminishes the accession of arterial blood to the brain, diminishes also the former of these, while ligatures around the external jugulars much enfeeble the latter. In the ordinary condition of the cranium this pressure is reflected back upon the brain.

"In conclusion, I believe it to be most important to bear in mind, when considering various pathological states of the brain, that its substance not only contains a variable amount of blood at different times, but that it is also subjected to a constant vascular pressure. This pressure arises partly from arterial and partly from venous distension: also, it is increased during expiration, and diminished during inspiration: and although the substance of the brain is very unyielding and incompressible, nevertheless it sustains, and is influenced by, this vascular pressure. I consider it essential, in studying the physiology or pathology of the brain, to have constantly in remembrance the existence of this vital force. Now vital forces, just as the most efficacious remedies, when they exceed or fall short of their proper amount, are capable of producing the most serious ill effects in the animal economy. Numerous causes may affect this momentum of the blood in the vessels of the head, and hence give rise to very different degrees of vascular pressure: at one time it may become excessive, oppress the organ, and suspend its functions: at another time, it is insufficient, and seems to be inadequate to sustain the cerebral functions. The injurious effects of modifications of this pressure on the brain would be much more often exhibited, were it not for the ample development of the venous system in the cranium and spinal canal, which affords such ready exit for redundant blood; and for another peculiarity in the anatomy of the parts contained in the cranium. The peculiarity to which I now advert, is rarely pointed out by teachers, and is not sufficiently estimated by pathologists. I allude to the large amount of extra-vascular fluid in the cranium, even in health, and which, in the form of serum is found in the ventricles and membranes of the brain, as well as disseminated through its substance. This fluid, very appropriately designated cephalo-rachidean, or cerebro-spinal, varies greatly in amount at different times: and, from the anatomy of the parts, as well as from experiments, it would appear that a portion of this fluid readily changes its site froin the cranium to the spinal canal, and conversely." P. 50.

The existence of this serum during life has been shown by the experiments of Magendie, Longet and others, and anatomy exhibits the free communications which exist between the ventricles and the cavities of the

spinal and cerebral membranes. The vivisections of Ecker and others show us also that the situation of this fluid may be subjected to considerable change by modifications of pressure. Dr. Burrows regards this fluid as supplemental to the other contents of the cranium-increasing or dimi. nishing in quantity inversely to the quantity of blood and serous matter contained within it. It may also be a means of equalizing pressure over the whole cerebro-spinal mass. When arterial or venous congestion of the brain is suddenly induced, the increased pressure which is exerted expels a portion of this serum into the spinal canal, while, when blood is abstracted from the cranium, the vacated cranial space is occupied by the spinal serum. When the cranium is healthy and normal, the cerebral substance may in this way accommodate itself to a temporary increase of blood; but when the increased determination to, or obstruction of return of blood from, the brain becomes more permanent, or the cranium contains other abnormal substances, the additional pressure will not be borne. Whenever there is an increased amount of solid matter in the cranium, whether from hypertrophy, tumours, extravasation, &c., whatever excites the heart's action and temporarily increases the degree of vascular pressure must increase the disturbance of the functions of the brain. "It seems to me probable that many permanent structural lesions within the cranium do not affect the functions of the brain by pressure, except when there is some cause in operation capable of inducing vascular congestion, or when the lesion is of a mechanical nature, or is gradually increasing."

On the other hand, whatever diminishes the heart's power in these morbid conditions of the brain mitigates the cerebral symptoms; but if such deficiency prevails in the healthy state of the brain, this organ suffers then from insufficient vascular pressure, and syncope results, this state being produced by such deficient pressure of the brain, and not, as usually supposed, from the inadequate supply of blood furnished to it. Thus, in its most simple form, it may be induced by a mere moral emotion diminishing the heart's energy, so that the blood is not propelled with sufficient energy to maintain an adequate pressure upon the cerebral substance. On account of the additional labour imposed upon the heart, the syncope is more likely to occur if the person is erect, and is relieved by his assuming the horizontal posture. The greater rapidity with which this state is induced by the abstraction of blood in the erect posture proves that the posture rather than the amount of blood lost is the efficient cause.

"I am the more anxious to direct attention to the foregoing explanation of the phenomena of syncope, because a very different opinion has been advanced. in a recent work (Lib. of Medicine, Vol. 2) in extensive circulation among the junior members of the profession. Thus, in an Essay on Apoplexy (p. 92), it is asserted that syncope differs from apoplexy only in the extreme feebleness of the heart's action; but the cause producing loss of consciousness, sensation, and motion, is stated to be the same in both affections. In either case, it is said, owing to the peculiarities of the circulation within the cranium, pressure is exerted on the brain; and in some cases it is difficult to distinguish the states of apoplexy and syncope from each other. Thus either from increased or diminished action of the heart, pressure on the brain may be produced by over-distension of its vessels; in the first case, of its arteries, and in the second, of its veins.' Here we find it promulgated that apoplexy and syncope are to be attributed to the same physical cause, viz., pressure on the brain; and that in syncope

1846.]

ON VASCULAR Pressure within the Cranium.

39

the pressure arises from the diminished action of the heart occasioning fulness of the cerebral veins. Now, I believe, that so far from syncope being occasioned by pressure on the brain, it will be found, as I have stated at some length, that every method of diminishing vascular pressure on the brain to any great extent, whether it be accomplished by depressing moral emotions, by sudden loss of blood, by the erect posture of the body, or by contrivances which diminish the momentum of the blood flowing towards the brain, will almost certainly induce syncope.

"But if syncope be produced by venous congestion, causing pressure on the brain, would any practitioner of experience attempt to overcome it by the use of those remedies most likely to diminish venous congestion of the brain, and the consequent pressure on that organ? Would he be bold enough to place his fainting patient in the erect posture, or draw blood from the jugular vein? I have also shown by experiments, that when an animal is bled to the point of fatal syncope, that, so far from finding venous congestion of the brain after death, all its vessels are, on the contrary, ex-sanguine. It appears to me, that syncope differs from apoplexy in every respect but in this one, viz., that in both there is a total temporary abolition of the functions of the brain. The causes producing the abolition, and the means to be employed to restore the functions of the brain, are generally quite opposite. Without presuming to be hypercritical, there is cause to regret that such erroneous doctrines as to the nature of so alarming a condition of the system as syncope should have been disseminated by modern writers." P. 64.

Dr. Burrows does not attribute the disturbance of the functions of the brain which takes place in anæmia, so much to the actual deficiency of blood in the organ, as to the defective amount of vascular pressure exerted upon it. Thus, in anæmia from hypertrophy of the brain, in which the dense cerebral mass is dry and destitute of blood, none of these symptoms are present: but in general anæmia, resulting from loss of blood, the various severe nervous symptoms are all at least temporarily mitigated by posture, stimuli, and whatever favours the momentum of the blood entering the brain.

The effects which have resulted from the ligature of one or both carotids also illustrate the doctrine here laid down. Mr. Key tied the right common carotid in a woman æt. 61, and she died in four hours, having manifested stertorous breathing. The carotid on the right side was found nearly obstructed and the vertebrals small. The brain was healthy, and the sudden diminution of the momentum of the blood in the cerebral arteries seems the only mode of explaining her rapid death. Although such a result does not usually follow the ligature of one common carotid, yet a reference to the numerous cases, collected by M. Longet and Dr. Chevers, show the frequency of the speedy supervention of marked disturbance of the cerebral functions or the subsequent occurrence of hemiplegia dependent upon cerebral disorganization.

"These subsequent phenomena appear to me to arise from two causes; partly from the insufficient supply of blood to the disorganized hemisphere of the cerebrum, and partly from the compression of the exsanguined hemisphere by its fellow, the vessels of which still continue to be liberally supplied with blood. In healthy states of the circulation within the cranium the forces distending the blood-vessels in either cerebral hemisphere are equal, opposite, and counterbalance each other: but so soon as the free supply of blood to one hemisphere is cut off by the ligature of the common carotid, the vascular distension in the other hemisphere becomes a source of pressure on the exsanguined side.