With respect to the means by which the animalization of the chyle is perfected after it enters the vessels, we have no certain informa tion, and we have scarcely any analogy which may assist in guiding our opinion. What is termed by modern physiologists the action of the vessels, by which so many operations of the animal economy are supposed to be effected, we may regard rather as an expression which serves as a convenient veil for our ignorance, than as throwing any light upon the process. We have no evidence that any addition is made to the chyle while in the. lacteals ; and indeed we can scarcely suppose it possible that this is the case, so that the only conceivable effect of this action is reduced to the motion which is imparted to the chyle by the alternate contrac tion and relaxation of the vessels, in conse quence of which the constituents may be more completely mixed together, and to a certain degree of pressure and temperature to which it is exposed, which may modify any spontaneous change that might otherwise take place in the arrangement of its elements. But to whatever cause it may be referred, we must consider the chemical and physical change in the nature of the chyle as one effect produced by the lacteals, as well as the progressive motion which is im parted to their contents.
In the present state of our knowledge on the subject, it remains for us to consider whether we have any independent evidence of the exist ence of the muscular fibres of the absorbent vessels, whether, if their existence be proved, and their contractility thus established, it would be necessary for us to search out for other causes of the effects, and lastly, to what other principle the acknowledged effects might be attributed, should it appear, upon full con sideration, that the assigned cause is insufficient or inadequate.
The above considerations lead us to give an account of the hypothesis of the action of the absorbents, which has been proposed by M. Magendie. He had ascertained, by a previous train of experiments, that according to the con dition of the system as to depletion or plethora, the process of absorption was respectively acce lerated or retarded. Hence he draws the con clusion, which, however, we conceive not to be a necessary consequence of the premises, that the function depends on a mere mechanical principle, independent of any vital action. The mechanical principle to which he has recourse, and which lie thinks can alone account for the effect, is that of capillary attraction ; but this he conceives not to take place from the open mouths of the vessels, according to the ordinary conception of the but that the fluid is imbibed by the substance of the vessel itself, and is, as it were, filtered through its pores.* He explains its further progress by supposing, that when it has entered these pores, it is car ried forwards by the current of the fluid pre viously in the vessel.
To prove his idea of the permeability of the parietes of the vessels, he instituted a series of experiments on the veins of an animal shortly after death, when he found that they were capable of imbibing and transmitting certain fluids with which they were placed in contact. Still farther to substantiate the hypothesis, M. Magendie repeated a set of analogous ex
periments on the vessels of a living animal. They consisted essentially in detaching a por tion of one of the great veins, and applying to its surface the solution of some narcotic or poisonous substance, the effects of which were, in a short time, manifested in the system at large.* This doctrine of imbibition and transudation has been embraced by M. Fodera, who has endeavoured to confirm the opinion of M. Ma gendie by additional experiments, which he conceives tend directly to prove that the vessels of the living body possess this power of im bibition. The method which he adopted to prove this point, in the most unequivocal man ner, was to inject into two separate cavities of the body two fluids, which by their union pro duce a compound, the presence of which may be easily detected, and which could be formed by no other means except by this union. For example, into the cavities of the pleura and the peritoneum were respectively injected the solutions of the ferro-prussiate of potash and of the sulphate of iron, when it was found, after a certain length of time, that various membranes and glands, connected with the thorax and the abdomen, were tinged with a blue colour.
M. Magendie afterwards performed an ex periment, which seemed more directly to bear upon the question, where a solution of the ferro-prussiate was retained in a portion of the intestine, at the same time that its external surface was placed in contact with a solution of the sulphate of iron : the part was then ex posed to the galvanic influence, the result of which was that a blue tinge was communicated to the sulphate. We are further informed, that according to the direction of the galvanic cur rent, the blue colour was produced either in the sulphate or in the ferro-prussiate. From these experiments M. Fodera draws the con clusion, that the processes of absorption and of exhalation may be referred to the mechanical operations of imbibition and transudation, which take place through the pores or capillary open ings of the various textures of the body.t On these experiments, and the conclusion deduced from them, we shall remark, that the facts appear to prove that membranes, perhaps during life, and certainly after death, before any visible decomposition has taken place, are capable of transmitting fluids through their tex ture; but we conceive that the analogy between this case and that of the entrance of chyle into the lacteals is so incomplete, that we can draw no inference from the one of these events which can be fairly applied to the other. Both the mechanical and the physiological properties of membranes and vessels differ much from each other, while the nature of the fluids employed in the experiments is totally different from any thing to which the parts are exposed under ordinary circumstances. It may be further remarked, that if the texture of the vessels is so permeable to fluids of all kinds and in all directions, it is difficult to conceive of any cause which can retain them there when they have entered, and which should prevent their escaping through the same pores when any pressure is made on the contents of the vessels by its contractile power or by any extraneous force.