Physiological Researches on Life and Death

by Xavier Bichat

2dly, I opened the carotid artery of a dog; the red blood instantly gushed out, but was immediately suppressed, and the artery tied. I then killed the creature, by striking him with violence on the occipital bone.[117] The animal life, and consequently both the mechanical and chemical functions of the lungs, were suddenly suppressed. The artery was then united. It poured forth the black blood with a feeble jet, for some little time, and after some minutes, the heart entirely ceased to move.

3dly, I have always obtained a similar result in opening the arteries of different animals which I afterwards killed, either by dividing the marrow between the first vertebra and occiput, or by strongly compressing the brain, which I had previously exposed.—It is thus also that animals perish, by the carotids of which a deleterious substance has been injected.

4thly, The preceding experiments explain the reason why the blood is black which flows from the arteries of animals, which are bled in our slaughter-houses, after having been knocked in the head. If the blow has been violent, the blood issues such as it was in the veins, but if the action of the diaphragm and intercostals has only been weakened by the blow, the redness of the blood is only diminished.

The state in which the respiration may be (and it is altered from a variety of circumstances during profuse hemorrhagy) occasions a great variety in the colour of the arterial blood: hence we have the reason why it is found of so many different shades in the great operations of surgery. At the beginning of these, it often flows out quite red; at the end of them, is sometimes almost black. The easy or embarrassed state of the respiration of the patient, is the occasion of these varieties. This I have frequently remarked, when attending Desault, and was often struck with the appearance, before I knew the cause of it.

I have never found any relation whatever, between the obscure colour of the blood, and the compression exercised above the artery, as some have asserted to take place. There is, indeed, a connection between the colour and the impetuosity of the jet, but the reason of this is evident to any one who has read the foregoing pages.

To return to the point of doctrine on which we are at present occupied, I am persuaded from the considerations and experiments which are adduced in the course of this chapter, that the manner in which the heart ceases to act, when the cerebral functions are suspended, can no longer admit of a doubt, and that we may resolve the question proposed, in affirming that under such circumstances, the death of the heart is occasioned through the medium of that of the lungs.

There is this difference, then, between the death of the heart, in consequence of that of the brain, and the death of the brain in consequence of that of the heart, that the one is indirect, the other direct, as we have already seen. If some men, as Stahl asserts, have really been able to suspend the movements of the heart, the fact is not a proof of the influence of the mind over the muscles of the organic life, but of its power over the mechanical, and consequently, the chemical phenomena of respiration.

In red and cold-blooded animals, the death of the heart does not succeed the death of the brain so quickly as it does in red and warm-blooded animals. Cut off the head of a frog, and the heart will continue to beat for some time afterwards. This phenomenon will be easily accounted for, if we recollect that respiration with these animals may be suspended a length of time, without arresting the movements of the heart.

In fact, as the heart dies only because the lungs die in the first place, when the cerebral functions are interrupted, it is plain that there ought to exist between the violent death of the heart and that of the brain, an interval nearly equal to that during which, in the natural state, there may be a suspension of respiration.