Physiological Researches on Life and Death

by Xavier Bichat

2dly.—The natural strength of the arteries, though enfeebled by the influx of blood into their parietes, is much superior to that of the veins, which besides are subject to the same cause of debility.[89] Accordingly these vessels and the aortic ventricle, are capable of surmounting the resistance of the capillary vessels of the body in general, much more easily than the veins and the venous ventricle, are of vanquishing the capillaries of the lungs.

3dly.—In the general capillary system, there is only one cause of want of action, viz. the presence of black blood in it; to this in the lungs there is added another cause, the want of that habitual excitement which this organ receives on the part of the atmospheric air: accordingly in the lungs, there is a greater resistance offered to the influx of the blood, and with respect to the heart, a less capability of surmounting such resistance. In the other parts, the contrary of all this is observed, a less resistance to the influx of the blood from the arteries into the veins on the one hand, and on the other a greater capability of overcoming such resistance.

4thly.—In the general capillary system, which is continued on from that of the arteries, if the circulation be embarrassed at first, in any organ in particular, it may still continue to go on in the other organs, more or less, in which case the blood regurgitates by these others into the veins. On the contrary, as all the capillary system, which is the continuation of the general venous system, is concentrated in the lungs, the venous circulation must be suppressed, whenever this organ loses its powers.

The preceding considerations, if I am not mistaken, explain why the vascular systems are so unequally full of blood after death, a circumstance, which is common to almost every disease, as well as the asphyxiæ.

In the latter sort of death however, although the general capillary system presents a less degree of resistance than is made by the capillary system of the lungs, nevertheless such resistance arising from the influx of the black blood into the organs in general is very manifest, and produces two remarkable phenomena.

The first is a greater quantity than usual of black blood in the arteries, and therefore a greater difficulty of injecting these vessels. Such blood is seldom coagulated. Indeed in all cases the venous blood is much less coagulable than arterial blood. This fact is proved, 1st, By the experiments of modern Chemists. 2dly, By the comparison of the blood of varices with that of aneurisms. 3dly, By the inspection of that which usually stagnates after death in the veins of the neighbourhood of the heart.

The second circumstance, to which I have referred, is the general livid colour of the greater number of the surfaces, with the fulness of divers parts, such as the face, the tongue and lips. These two phenomena indicate a stagnation of the blood at the extremities of the arteries, in the same way as they denote the same effect in the pulmonary vessels; here there is a much more evident repletion, because as I have said, the capillary system is there concentrated within narrow limits.

The reflux of the blood of the veins towards the extremities is the reason assigned by authors for the livid appearance of asphyxiated persons. There is little reality in this cause: in fact, this reflux, which is very sensible in the trunks of the veins, diminishes continually towards their ramifications, where it is impeded and rendered impossible by the valves, besides which, the following experiment is an evident proof, that we must attribute the lividity in question, to the impulse of the black blood from the aortic ventricle.

1st.—Adapt a syringe with its stop-cock to the divided trachea. 2dly, Open the abdomen so as to distinguish the intestines and epiploon. 3dly, Shut the cock. At the end of two or three minutes, the red tint which animates the peritoneum, and which is borrowed by this membrane from the vessels, which creep underneath it, will be changed into a dull brown colour. This colour may be made to disappear and re-appear at will, by opening or shutting the syringe.