enter into either of these organs, the essence of the experiment is destroyed. And, even granting that all these difficulties could be counteracted, still it would by no means follow, that because an active chemical solution can pass through a membrane, or the coat of a vessel, that the same could be done by the chyle. I feel, therefore, no hesitation in asserting that, curious and interesting as are the experiments of M. Fodera, they do not prove the position which they profess to establish; and that they ought not to affect our ideas respecting the doctrine of absorption.3

We are indebted to Dr. Barry, whose observations on respiration I have already had occasion to refer to,

3 It is but justice to M. Fodera, to remark, that the full detail of his experiments, so far as I am able to learn, has not yet been given to the public. I think, however, that it is not unfair to conclude that the report of them, which is inserted in M. Magendie's journal, may be regarded as exhibiting a correct account of them; and that no circumstance would be omitted, which could be fairly urged in their favour.

• Since I wrote the short appendix to the 7th chapter, I have had the pleasure of perusing the detailed account of Dr. Barry's experiments, together with the report of them made to the Academy of Sciences, by MM. Cuvier and Duméril; and I had likewise the good fortune to be present at some experiments which were performed by Dr. Barry himself, at the Veterinary College. Making those allowances for unforseen and unavoidable difficulties, which it is but fair to admit on such occasions, I should say that it appeared sufficiently obvious, that when one end of a glass tube was inserted either into the large

* Recherches experimentales sur les causes du mouvement du sang, &c.

for a series of experiments which he performed in order to prove, that absorption depends altogether upon atmospherical pressure. The experiments, which appear to have been sufficiently numerous, and to have been attended with very decisive results, consisted in introducing into a wound a portion of some poison, the effects of which had been previously ascertained, and to compare these with what took place when the pressure of the atmosphere was removed, by the application of an exhausted cupping-glass over the wound. results appear to have been very remarkable; and, in a practical point of view, cannot fail to prove of great and obvious utility. The same dose of poison, which,

The

veins, into the cavity of the thorax, or into the pericardium, the other end being plunged into a vessel of coloured water, the water was seen to rise up the tube during inspiration, and to descend during expiration. We may hence conclude, that under the circumstances in which the experiment was performed, there was less resistance to the entrance of the venous blood into the heart during inspiration than during expiration; but it will still remain for us to inquire whether the principle will apply to the organs in their natural and entire state, or in what degree it is applicable. Now, there are some facts, which would lead us to suppose, either that the effect does not take place, or that it does so in a very slight degree only. 1. During each act of respira tion, we have three or four pulsations of the heart, which are exactly of the same strength, although they must have occurred during the various states of the thorax. 2. In the fœtus, where the lungs are quiescent, we have still the circulation proceeding without any apparent difficulty. 3. There are various tribes of animals that possess a circulating system; but which are either without lungs, or have them constructed upon a principle entirely different from those of the mammalia.

under ordinary circumstances, destroyed an animal in a few seconds, was rendered completely harmless by the operation of the vacuum; and when the symptoms had commenced, and even when they had proceeded so far as to impress the spectators with the idea that the life of the animal was destroyed, still the vacuum had the effect of speedily and entirely removing them ".

Important, however, as these experiments are in a practical point of view, there appear to me to be certain circumstances, which must be taken into account before we can admit of the hypothesis that is deduced from them. In the first place, it would seem that the poison was not simply laid upon the surface, but was inserted into a wound; hence it would be immediately mixed with the blood, and be carried by the veins to the central parts of the system. Now, it is obvious, that when a vacuum is formed over the divided end of a vessel, and especially of a vessel which is supposed to be passive, or to be influenced only by physical causes, the motion of the fluid through this vessel

5 Dr. Barry presented an account of his experiments on absorption, and of the inferences which he deduced from them, to the Med. Chir. Society; it is from this source that I derive my information. The following are two of Dr. Barry's positions :

That the whole function of external absorption is a physical effect of atmospheric pressure." "That the circulation in the absorbing vessels, and in the great veins, depends upon this same cause, in all animals possessing the power of contracting and dilating a cavity around that point, to which the centripetal current of their circulation is directed." Dr. Barry explicitly states his opinion, that vital action is not concerned in absorption.

must be retarded. And this would be equally the case, upon whatever principle we supposed the fluid to be propelled, or carried through the vessel in question.

But it does not necessarily follow that this would be the case in the natural state of the parts, when the vessels remain entire, and the atmospheric pressure is exercised equally upon all the contiguous organs. Nor does it appear to be an obvious consequence of Dr. Barry's experiments, that the same effect would ensue, if we had it in our power to apply a poisonous substance to the extremity of a lacteal or a lymphatic, provided as these vessels are with valves, and exercising a contractile power over their contents. The immediate effect would be the distention of the contiguous parts, and the dilatation of the vessel itself; but, provided the extremity of the vessel remained closed, this operation might promote, rather than retard, the progress of its contents.

In the last place, I conceive that it is altogether impossible to apply Dr. Barry's principle to the action of the lacteals; they appear to be so far removed from the influence of atmospheric pressure, that we must suppose their contents to be propelled by some inherent power in the vessels themselves, or by some mechanism immediately connected with them; and presuming this to be the case, we have a very strong analogical argument for supposing, that the function of absorption, in the other parts of the system, is conducted upon the same principle.

When we examine the extent of the lymphatic

system, and endeavour to trace out its connexion with the various parts of the body, we observe that a great number of these vessels have their origin from the neighbourhood of the cutis," and it has therefore been supposed that absorption is carried on to a considerable extent by all parts of the surface. The doctrine of cutaneous absorption seemed to explain a great variety of phenomena in the animal œconomy, both physical and pathological, and was generally had recourse to as one of those operations, which had a powerful influence upon the functions of the body, both in their natural and their morbid condition. That under certain circumstances the absorbents are able to take up substances applied to the skin, especially when aided by friction, is sufficiently proved by the effect of various medical agents which are enabled by this means to enter into the circulation, and to act upon the system in the same manner as if they had been received into the stomach. Thus mercury applied to the surface produces its specific effect upon the salivary glands, and lead upon the muscular fibre, while opium, tobacco, and other narcotics, manifest their peculiar action upon the nervous system.

But besides this absorption of substances applied to the skin, and forced into the mouths of the vessels by friction or other mechanical means, it was an opinion very generally embraced by physiologists,

6 We have a view of the cutaneous lymphatics, as far as they can be rendered visible by injections, in Haase, de Vas. Cut. et Intest. Absorb. tab. fig. 2; also in Mascagni, tab. 2. fig. 9..28. and tab. 3.