It has been asserted by Bichat^[11] that the immediate cause of death, when it takes place suddenly, must be the cessation of the functions of the heart, brain, or lungs; although it is sometimes difficult to determine which of these organs is the first to fail in its action; this may be well exemplified by the poisonous operation of Arsenic upon the animal economy, which when introduced into the circulating system will, according to the valuable experiments of Mr. Brodie, occasion stupor and paralysis, a feeble and intermitting contraction of the heart, and slow and laborious respiration; but it is found that in some cases, one order of symptoms will predominate, and be the first to display themselves, whilst in others, the very contrary will obtain, without perhaps our being able to assign the immediate cause of such deviations. There are, moreover, cases of sudden death, in which the principle of animation would seem to be at once annihilated in every part of the animal machine, and when every organ appears to be simultaneously affected, as in that occasioned by the agency of intense cold, and sometimes, for it is not in every instance, by that of lightning, or electricity; still, as a general proposition, the aphorism of Bichat must be admitted; and we shall proceed to investigate the subject of sudden death, as connected with medico-judicial inquiry, upon principles deduced from the enlightened views of this distinguished philosopher. To the able and satisfactory researches of our English physiologist, Mr. Brodie, we are also greatly indebted for a correct notion of the nature and order of succession, of those events by which life is quickly extinguished; his attention was many years ago directed to one important branch of this subject,—to the investigation of that series of changes produced on living bodies by the operation of poisons, the results of which were published in the Philosophical Transactions,^[12] to which we shall have frequent occasion to refer in the following pages. Since that period he has diligently pursued the subject in its more extensive ramifications, and in his lectures, delivered from the anatomical chair of the College of Surgeons during the last year, he presented a condensed and philosophical history of the phenomena of death, in general, in which he elucidated many leading points that were before obscure, established several propositions that have long been considered doubtful, and rejected a mass of popular error, which, under the sanction of authority, has continued to retard our inquiries, and to embarrass and misguide our practice. The author of the present section of this work has to acknowledge the kindness and liberality by which he is enabled to avail himself of these luminous researches, having been furnished by his friend Mr. Brodie with the manuscript notes from which the lectures were delivered.

The organs more immediately necessary to life are, the Heart, which conveys to every part of the body that fluid, without a constant supply and change of which, vitality must be speedily exhausted; and the Lungs, by whose functions this essential fluid undergoes those unknown changes, from the action of the atmosphere, which adapt it for the performance of the important duties to which we have alluded.

In conformity with these views, the functions of the heart, and their connection with those of the lungs and brain, very naturally present themselves as the first objects of physiological inquiry; and there is certainly no discovery in modern times more interesting in its relations, and at the same time so useful in practical application, as that which has determined the nature of the connections between the functions of respiration and the motions of the heart; and shewn why the cessation of the former should occasion the destruction of the latter. The existence of this mysterious connection constituted a subject of interest and inquiry in the more remote ages, and it will not be unprofitable to take a review of the different theories which have been proposed for its explanation. Until the celebrated experiment^[13] of Hook, it was supposed that the heart’s motion was maintained by the alternate contraction and dilatation of the lungs in the act of breathing; but the extraordinary philosopher above mentioned decided this point by exposing the thorax of a dog, and separating the pleura extensively from the external surface of the lungs, and then, by means of a pair of double bellows, keeping up a constant stream of air through the air cells; by this contrivance respiration was duly performed, while the lungs remained motionless, and yet it was found that the vigour of the heart’s action was not in the least impaired; whereas, if the theory which Hook undertook to refute, had been founded in truth, the heart, under such circumstances, must necessarily have become quiescent. Mr. Hunter^[14] supposed the existence of a sympathy, or association, between the motions of the heart and lungs; and the same opinion appears to have been entertained by Dr. Currie^[15]; Dr. Darwin^[16] deduced the existence of this immediate connection from that general law of the animal œconomy, by which motions that are frequently repeated in succession acquire the power of recurring in the same order, independently of the original exciting cause; “it is thus,” says he, “that by the stimulus of the blood in the right chamber of the heart the lungs are induced to expand themselves.” Dr. Bostock^[17], however, has very satisfactorily opposed this hypothesis, by observing that in the fœtus the heart commences its contractions immediately upon its formation, while the lungs remain perfectly at rest; and that when the animal leaves the uterus, the motion of the lungs commences, but the periods of the contraction of the diaphragm bear no determinate ratio to those of the systole of the heart.

It was long supposed that the cessation of respiration occasioned that of the heart’s motion, in consequence of the black blood not having sufficient power to stimulate its fibres; but does not the right side of the heart, which, under all circumstances, contains de-oxygenated blood, contract with a vigour equal to that of the left? It was reserved for Bichat to offer a true explanation of this phenomenon; he has very justly stated that, in consequence of the suspension of the respiratory function, the coronary vessels, by which the muscular structure of the heart is supplied, are compelled to carry black, instead of scarlet blood; a fact which in itself is quite adequate to explain the cause of the heart ceasing to contract; for the irritability of this, like that of every other muscle, can be alone maintained by duly oxygenized blood. But it remains to be shewn how the functions of the brain and nervous system stand related to those of the heart and lungs. Although the agency of nervous influence is necessarily involved in impenetrable obscurity, yet we shall not have much difficulty in proving, that the brain^[18] is immediately necessary to life only because the muscles of respiration owe their action to its influence. M. Lallemand has published the history of a fœtus, in which the brain and spinal marrow were equally deficient, notwithstanding which, it even exceeded the usual size, the heart was perfect, and it was evident that the circulation had been properly performed; no sooner, however, was the monster born than it perished, because the diaphragm and other muscles of respiration were unable to perform their functions without the aid of nervous excitement; no air was therefore inhaled into the lungs, and in a few minutes the heart ceased to contract from the deficient supply of oxygenized blood. If the phrenic nerves of a quadruped be divided,^[19] the motion of the diaphragm ceases, and the animal breathes by the motion of the ribs alone, panting and respiring with difficulty and distress. If the spinal marrow be divided below the origin of the phrenic nerves in the lower part of the neck, no interruption is given to the transmission of the nervous influence to the diaphragm, but the ribs now become motionless, and respiration is performed by the diaphragm only; if the spinal marrow be divided in the upper part of the neck, above the origin of the phrenic nerves, the nervous influence is neither transmitted to the diaphragm, nor to the muscles which produce the motion of the ribs, and respiration is entirely suspended; under these circumstances the heart continues to contract for some minutes, after which it ceases, as there is no supply of blood which has received the influence of the air, and, consequently, the muscular fibres of the heart lose their excitability, and the blood is no longer circulated; if, however, the lungs be artificially inflated, before the action of the heart has ceased, its motions are continued. The experiment may also be very satisfactorily varied in the following manner; apply a ligature to the carotid arteries in the neck, so as to prevent the occurrence of hemorrhage, and then decapitate the animal; if respiration be now artificially maintained, the heart will suffer no disturbance in its motions, but the circulation will be preserved for several hours in the body of the decapitated animal. In further illustration of this view of the subject, Mr. Brodie observes, that many reptiles which are capable of respiring by means of the skin, will survive the loss of the brain for so long a period, that the wound made by decapitation, becomes cicatrized, and death only takes place at last in consequence of inanition.—(Manuscript Notes.)

In farther illustration of these views, let us observe the mode in which death takes place in apoplexy, or in cases of pressure on the brain, whether occasioned by a depressed portion of bone, or by blood extravasated within the cranium. At first the patient is insensible to all external impressions, but the breathing is not affected; after an interval, however, the respiration becomes difficult and laborious, and the purple hue of the lips and cheeks, from the sub-cutaneous vessels, demonstrates that the blood is imperfectly oxygenized. The arterial action becomes more slow, in proportion only as the respiration is more difficult; and the pulse may even be distinguished at the wrist, after the breathing has altogether ceased; under such circumstances it is obvious that life might be protracted for several hours by artificial inflation of the lungs, but as no ultimate benefit could be derived from such an operation, its expediency may be fairly questioned.

Enough has been said to shew that the brain is not immediately necessary to the action of the heart; but Mr. Brodie has very justly observed that the general proposition thus established, must not lead us to the conclusion that the heart is therefore incapable of being affected by violent impressions on the nervous system; the fact is quite otherwise, for although the brain may be removed, and the circulation be nevertheless maintained by artificial respiration, yet an injury inflicted on the brain, of another kind, may be followed by those immediately fatal consequences which decapitation itself would not produce. Dr. Wilson Philip states that if the brain be violently crushed, the action of the heart is immediately stopped; and the fact is too notorious to be questioned, that a blow on the head is frequently succeeded by Syncope; there are but few circumstances, says Mr. Brodie, in the history of the animal œconomy which appears more remarkable than this fact, that an injury of a part which is not immediately essential to the heart’s action, should nevertheless, under certain circumstances, have the effect of occasioning its immediate cessation. The late researches of Le Gallois may perhaps receive farther elucidation from the above proposition; this physiologist has stated that if a wire be introduced into the Theca vertebralis, and be moved upward and downward, so as to destroy the texture of the spinal marrow, the action of the heart presently ceases; and he from thence advances to the conclusion, not only that the spinal marrow is necessary to the heart’s action, but that every part of the animal body derives its vital properties from it; from what I have observed, says Mr. Brodie (Manuscript Notes) in the repetition of the foregoing experiment, I should infer that the fact is correctly stated, as far as it relates to warm-blooded animals, but the conclusions are undoubtedly premature; and the history of the fœtus, as related by Lallemand, in which, notwithstanding the absence of the brain and spinal marrow, the child was even larger than usual, the heart perfect, and it was manifest that the circution had been duly performed, is in direct opposition to such a theory. We must here agree with Mr. Brodie, that such phenomena are quite incompatible with the doctrine in which the spinal marrow is supposed to be directly necessary to the existence of vitality in the system generally, and to the action of the heart in particular; and that we must therefore look for some other explanation of the effects which are produced by the destruction of the spinal marrow in warm-blooded quadrupeds.—May they not be explained by supposing them to be the effect of the shock which must necessarily attend the removal of the spinal marrow, which can never be effected with the facility that attends decapitation?

We have deemed it necessary to offer these few remarks upon the relations which subsist between the functions of the heart, lungs, and brain, in as much as the propositions which have been thus established respecting them, can alone lead to a correct pathology of those diseases, by which life is suddenly extinguished, or suggest a rational and effectual plan of treatment, in cases of suspended animation.