Physiological Researches on Life and Death

by Xavier Bichat

Before the lymphatic vessels were known, the principal phenomena of absorption were observed, and it was natural to attribute them to the action of the veins. This opinion was maintained for a long time after the discovery of the lymphatics. Finally, towards the middle of the last century, Hunter being engaged in examining these vessels, which he has done more to make known than any other man, thought that they should be considered as the agents of absorption, and this opinion was soon generally admitted. If we look for the means by which he overthrew the ancient theory, we are astonished to find that it was by five experiments only. Harvey did not with equal facility obtain the acknowledgment of the circulation, and perhaps there does not exist a second example of an opinion, which was for a long time established, being abandoned so readily. It should be remarked, that physiologists had not yet recovered from the surprise produced by the discovery of a system of vessels so extensive, and yet for so long a time unknown; they were impatient to know the use of them; the veins had already the function of returning to the heart the blood brought by the arteries; they thought it would not impoverish them too much to deprive them of the faculty of absorbing, in order to enrich the lymphatics with it. Of the five experiments of Hunter, two are designed to prove that the veins do not absorb, the object of the other three is to show that the lymphatics do.

In the first experiment he injected tepid water into a portion of intestine, and the blood which returned by the vein appeared to be neither more diluted nor lighter than before. We cannot conceive how by mere inspection, it is possible to judge if the blood contains a certain quantity of absorbed water, a quantity which must be proportionably very small, if we consider the whole amount of blood that passes through the mesentric veins during the period necessary for the absorption of the fluid. Hunter in the same experiment tied the artery which went to the portion of intestine, and examined the state of the vein. It did not swell, and its blood did not become aqueous. But after this ligature, did the absorption continue to go on in this portion of intestine, which still had no doubt lymphatic vessels? This the author does not say. How moreover should he think that the vein could continue its action when the artery was tied?

In the second experiment Hunter injected milk into a portion of intestine, and was unable to discover this fluid in the blood of the mesentric veins; but at the period in which this experiment was made, mankind were very far from being able to detect in the blood a very small quantity of milk, and at the present day, with all the aid derived from chemistry, we can hardly discover in it a small quantity which is mixed directly with it. These two experiments prove then nothing against the absorption of the veins; as to those which he brings forward in favour of absorption by the lymphatics, they are not more conclusive. I shall content myself with relating one of them. He injected, into a portion of intestine that was empty, a certain quantity of warm milk, and confined it there by two ligatures. The veins that came from this portion were emptied of their blood by several punctures made in their trunk. The corresponding arteries were tied. He then returned the parts into the abdomen, and drew them out again in half an hour. Having examined them with attention, he observed that the veins were almost empty, and that they contained no white fluid, whilst the lacteals were almost full of it. But was not this white fluid that filled them chyle rather than milk? Was it not there before the injection of this liquid? In order to ascertain what takes place in the lymphatic vessels during absorption, we must begin by examining the state of these vessels before the experiment. But this is what Hunter did not do, and it is this that renders his experiment of no value. It is not very astonishing that he mistook the chyle for the milk, since milk has for a long time been mistaken for chyle. Flandrin, Professor of the Veterinary School at Alfort, has several times repeated this experiment of Hunter; but he took care before the injection of the milk to ascertain that the lymphatics contained no white fluid; and he never found any in their cavity after the experiment. I have myself many times performed this experiment, with the same precaution, and I have uniformly obtained the same results as those of Flandrin.

It would occupy too much time to examine all the reasons that have been advanced for and against the absorption of the lymphatics; I shall only relate some experiments I have made myself; but I ought first to observe, that absorption undoubtedly takes place in parts such as the eye, the brain, and the placenta in which the most minute dissection has been unable to discover any lymphatic vessel.

First experiment.—Four ounces of the decoction of rhubarb was given to a dog, in half an hour after he was killed, and it was found that more than half of the liquid had disappeared; the urine evidently contained rhubarb, but the lymph in the thoracic duct exhibited no trace of it.

Second experiment.—A dog swallowed several ounces of alcohol diluted with water; at the end of a quarter of an hour, the blood of the animal had a very distinct odour of alcohol, but there was nothing of the kind in the lymph.

Flandrin made a similar experiment on a horse, to whom he gave half a pound of assafetida mixed with an equal quantity of honey. Six hours after, the horse was killed. The odour of the assafetida was very perceptible in the blood of the veins of the stomach, of the small intestines and the cœcum; but it could not be perceived in the lymph.

Third experiment.—A dog was made to swallow six ounces of a solution of Prussiate of Potash in water. In a quarter of an hour, the urine very evidently contained some of the Prussiate; but the lymph taken from the thoracic duct showed no appearance of it.

Fourth experiment.—I gave to a dog, in whom I had tied the thoracic duct, two ounces of a decoction of nux vomica. The effects of absorption were as rapid as if the duct had been open. After the death of the animal I satisfied myself, that the duct had been well tied, and that there was no other branch, as there sometimes is, by which the lymph could get to the subclavian vein.

I have varied this experiment by putting the poisonous fluid, into the rectum, the sacs of the pleura and peritoneum. The results have been uniformly the same.