Physiological Researches on Life and Death

by Xavier Bichat

Here we cannot, as if the experiment were made upon other parts, suspect that a reflux is propagated from the right ventricle towards the venous extremities, since the mesenteric veins, together with the other branches of the vena portæ, form a system apart, independent of the great black-blooded system, and having no communication with the cavities of the heart which correspond with this system.

But I shall touch again upon this subject. The above experiment is amply sufficient to prove, that the lividity of the surfaces of the body is owing to arterial impulse.

At present we are in a condition to explain how the lungs are more or less gorged with blood, more or less livid, and how the livid spots upon the different parts of the body are more or less marked accordingly as the asphyxia has been more or less prolonged: for it is evident, that if before death, the black blood have gone round the two systems ten or twelve times, it will inject the extremities much more than if it had made such circulation only two or three times; at each revolution, a greater or less quantity will be left in the extremities, for want of action in the capillary vessels.

In finishing this chapter I shall take occasion to observe, that the spleen is the only organ of the economy susceptible like the lungs of assuming a very great variety of volume. Scarcely is it ever found in the same state. It has been falsely supposed that there is a relation between the plenitude or vacuity of the stomach, and the inequalities of the spleen; but this is not the case, as I have said elsewhere. Such inequalities during the life of the body do not exist, and supervene only at the instant of death.

It appears to me, that they depend especially upon the state of the liver, the capillary vessels of which, are the continuations of all the branches of the vena portæ as the capillaries of the lungs are those of the great venous system. Thus, when the hepatic capillaries from any cause whatever are enfeebled, the spleen must swell and be filled with the blood, which cannot traverse the liver.[90] In such case, if I may so express myself, there is an isolated asphyxia of the abdominal vascular apparatus. The liver being to the spleen, what the lungs are to the black-blooded cavities in common asphyxia. The resistance is in the former, the stagnation in the latter. But this matter may be better understood hereafter. Experiments upon animals killed in different ways, would throw much light upon it, and these I purpose undertaking. By these means we may rigorously establish the analogy existing between the stagnation of the blood in the different branches of the vena portæ, and that which is observed in the general venous system, in consequence of various kinds of death. With respect to the spleen and its system of veins, in ordinary asphyxia, I have never remarked in it any peculiarity.

FOOTNOTES:

[79] It is not because the vessels of the lungs have become tortuous that the blood flows through them with difficulty, but because they are compressed. It was needless for Goodwyn to seek for reasons to prove, that the flattening of the lungs does not offer a mechanical obstacle to the course of the blood. If he had observed with attention the phenomena of respiration, he would have seen that this contraction, if it does not completely interrupt the circulation of the blood in the lungs, at least modifies it in a very remarkable manner. When the lungs contract, not only the bronchial cells are flattened, but the pulmonary vessels are compressed, and tend to expel the blood contained in their cavity. This fluid flows back then on one part towards the right ventricle by the pulmonary artery, and on the other it accumulates in the pulmonary veins before entering the left auricle. Hence we see that the jet by the carotid artery must increase rather than lessen in the last moments. But if the compression continues, as the capacity of the ramifications of the pulmonary artery is diminished as well as that of the veins of the same name, the quantity of blood which passes through the lungs is less, and the jet by the carotid necessarily decreases. The experiment related by Bichat is then entirely opposed to the opinion which he advances.

It is not only by influencing the course of the blood in the system of pulmonary vessels that the alternate motion of the thorax modifies the circulation. If we lay bare the jugular vein of a dog, we perceive that the blood does not move in its cavity from the sole influence of the right auricle, but in an evident manner from the influence of the motions of respiration also.

At each time that the thorax is dilated in inspiration, the vein is quickly emptied, flattened and its parietes are sometimes brought exactly against each other; it swells on the contrary and fills with blood when the thorax contracts. A similar phenomenon takes place in the venæ cavæ. In order to render it evident it is sufficient to introduce by the jugular vein into the venæ cavæ a sound of gum elastic; we then see that the blood flows through the extremity of the sound only during the time of expiration. A similar effect is observed if we introduce a sound into the crural vein and direct it towards the abdomen.