Physiological Researches on Life and Death

by Xavier Bichat

2dly.—There are different vessels in the œconomy which we may alternately bend or extend at pleasure: such are those of the mesentery, when exposed by an incision into the abdomen of the animal. Now in this experiment, which has been already made to prove the influence of the tortuous direction of the arteries upon the mechanism of their pulsation, if one of the mesenteries be opened, and then either bent or extended, in either case the blood will be thrown out with the same degree of violence, and in equal times will be emitted in equal quantities. I have always obtained the same result in this experiment which I have many times repeated. From analogy we might expect the same from the vessels of the lungs;[79] and from the following experiment it may be proved.

3dly.—Take a dog, cut the trachea, and adapt the tube of an injecting syringe to it, then make a vacuum in the lungs, and cut the carotid artery. It is evident, that according to the common belief, the circulation should be immediately suspended, in this experiment, since the pulmonary vessels from their ordinary state of distension, must have passed to the greatest possible degree of collapse, in consequence of the total abstraction of air; notwithstanding which the blood will be violently thrown out from the divided arteries for a certain time, and must consequently traverse the lungs: it will afterwards cease by degrees, but this, from causes which I shall explain hereafter.

4thly.—The same effect may be produced by opening, on both sides, the breast of a living animal, because the warm and rarified air of the lungs, will be more than balanced by the pressure of the colder air without;[80] now, neither in this case does the circulation experience any sudden change. For the sake of greater exactness, the little air remaining in the cells of the organ may be voided by a syringe.

Along with these observations let us place the facility with which the pulmonary circulation continues to be made, when collections of water, pus, or blood, are lying within the pleura, or pericardium. In these cases the air vessels are often prodigiously contracted, and consequently the vessels of their parietes doubled and bent.[81] If this state be taken into consideration, we shall have sufficient data for concluding that the tortuous disposition of the vessels, can never be an obstacle to the passage of the blood; and therefore, that the interruption of the mechanical functions of the lungs, can never directly put a stop to the action of the heart, though it may do so indirectly, in impeding the exercise of the chemical functions of the lungs.

If then we can determine why the heart remains inactive, when the latter phenomena are annihilated, we shall have resolved a double question.

Many authors have asserted that the death, which ensues after a too long continued inspiration, is owing to the mechanical distension of the pulmonary vessels by the rarified air, a distension impeding the circulation. But this reason also is as false a one, as that which we have already disproved. Inflate the lungs as powerfully as may be, then tie the trachea and open the carotids, and the blood will flow as impetuously as when the respiration was perfectly free.[82]

II. Why does the heart cease to act, when the chemical functions of the lungs are interrupted?

According to Goodwyn, the reason why the contractions of the heart are stopped, when the chemical functions of the lungs have ceased to be performed, consists in the want of that excitement which the red blood only can produce upon the red-blooded ventricle. This ventricle, says he, has not a sufficient stimulus in the black blood, and death is occasioned because it no longer is capable of transmitting any thing to the different organs. In this case death must happen, as it would from ligature of the aorta—precisely in the same way as when its source is exclusively in the heart. The other parts die only for want of blood, just as when in a machine, the principal spring being taken away, the others cease to act, because they are not put into action.

On the contrary, I am persuaded that there is a general affection of all the parts, whenever the chemical functions of the lungs are suspended; I am persuaded that the black blood continues to be pushed on for some time by the aorta, and that its influx into the organs is the occasion of their death; that the organs die in fact, not because they do not receive blood, but because they do not receive red blood; in a word, that they are penetrated by the material cause of their death; so much so, that we may asphyxiate any isolated part at will, by injecting it with venous blood while all the others shall continue to receive the red blood of the heart. At present I shall inquire into the phenomena of the contact of the black blood with the parietes of the ventricle, and refer the reader to the following chapters, for its effects upon the other parts.