Physiological Researches on Life and Death

by Xavier Bichat

It was proper to make the opposite experiment, that is to say to diminish the quantity of blood, in order to see if absorption would take place sooner. This took place in fact, as I thought it would; about half a pound of blood was taken from an animal; the effects, which did not usually appear till after the second minute, showed themselves in thirty seconds.

Yet it might still be suspected, that it was less the distension of the blood-vessels than the change of the nature of the blood that opposed absorption. To remove this difficulty I made the following experiment; a dog was bled copiously; the place of the blood which he had lost was supplied by water at the temperature of 40 degrees of the centigrade thermometer, and a certain quantity of a solution of nux vomica was introduced into the pleura. The consequences of it were as prompt and as powerful, as if the nature of the blood had not been changed; it was then to the distension of the vessels that must be attributed the want or diminution of absorption.

The consequences that may be deduced from the experiments I have just related will acquire new force, if we connect with these facts a multitude of pathological ones, which are every day seen; such as the cure of dropsies, engorgements and inflammations by bleeding; the evident want of action of medicines at the moment of a violent fever, when the vascular system is powerfully distended; the practice of certain physicians who purge and bleed their patients before administering active medicines to them; the employment of cinchona at the period of remission for the cure of intermittent fevers; general or partial oedema from organic disease of the heart or lungs, and the application of a ligature upon the extremities after a puncture or a bite of a venomous animal, to prevent the deleterious effects which are the consequence of it.

On the whole, I think, it may be concluded from the preceding experiments that the capillary attraction of the small vessels is one of the principal causes of the absorption called venous. If the lymphatics do not appear to enjoy in the same manner the faculty of absorption, it probably arises not from the nature of the parietes, the physical properties of which are nearly the same as those of the veins, but from the want of a continuous current in their interior.

In this note I have brought together the absorption of the gases and that of fluids. This resemblance holds only as it relates to the permeability of the textures by these two orders of bodies. As to the cause of the absorption of the two, it cannot be the same, since gases are not subjected to capillary attraction.[28]

[28] Note by the Translator of Magendie’s Additions.—In the preceding note M. Magendie has not done justice to Mr. Hunter. Without entering at all into the examination of the question, whether absorption is performed by the lymphatics or the veins, it is due to Mr. Hunter to contradict the assertion, that “he overthrew the ancient theory by five experiments only.” He was not a man who adopted his opinions loosely or on slight grounds, and in the present case he performed between twenty and thirty judicious and satisfactory experiments, in the presence of several physicians and surgeons. It is true that these were performed on five different animals only, but if the result were uniform, this number was as good as five thousand or any other one that could be named.

G. H.

(See Hunter’s Commentaries and Cruikshank on the Absorbents.)

[29] Those theories no doubt are very incomplete that are borrowed from hydraulics, and probably will be so for a long time; but it arises from this, that the science on which it is founded, hydrodynamics, is still but little advanced. A great advance will unquestionably be made in physiology, when we shall arrive at a knowledge of the course of a fluid in a system of canals, which have the same physical conditions as the system of arterial and venous vessels. But it will be a long time before science will have arrived at that point. Is it necessary for this to make no use, in the explanation of the circulation, of the few facts which are known upon the course of the fluids? Is it necessary to enter entirely into the field of hypothesis, to suppose in the small vessels a sensibility and a contractility which evidently do not exist in the large ones? I cannot believe it, and I think even that if this hypothesis should be true, and if there should be demonstrated for the capillary vessels, those properties which are attributed to them, and which would have an influence on the course of the blood, we should then know but one of the conditions of this very complicated problem, and this would not in any degree do away the necessity of knowing all the mechanical conditions.

[30] Even in reasoning according to the hypothesis of Bichat, and admitting the existence of this organic sensibility, it would always be inaccurate to say, that the contraction is uniformly in proportion to the sensation. How is it to be known in fact? Since this sensibility is not transmitted to a common centre, it might very well be excited without our being informed of it by any apparent effect. Sometimes also a very evident contraction would correspond to the slightest excitement.