purpose he procured it from the thoracic duct of dogs. In all the essential points his results agreed with those of Vauquelin. The chyle consisted of a coagulum of a pinkish appearance, containing fibres or filaments, and of a fluid part very similar to the serum of blood, except that, in the animal chyle, there was the oily or fatty matter, which floated on its surface like cream. The vegetable chyle generally bore less resemblance to blood than that derived from animal food; the latter was more disposed to become putrid, and upon the addition of potash, it evolved a quantity of ammonia, which was not the case with the vegetable chyle, while the oily matter was found in the animal chyle alone. The two species were of the same specific gravity, and contained the same weight of saline matter, but the solid residuum of the animal chyle, as obtained by evaporation, was considerably greater than from the vegetable chyle. When they were both submitted to destructive distillation, the vegetable chyle produced three times as much carbon as the animal chyle, whence we may conclude that the latter contains a much greater proportion of hydrogen and nitrogen. It is not improbable that in this case, the vegetable chyle was less completed or assimilated, in consequence of the animal being fed upon a diet, which was not natural to its digestive organs; for we observe that the chyle of the horse, as examined by Vauquelin, which must have been derived from vegetable food, was in a more

3 Med. Chir. Tr. v. vi. p. 618. et seq..

animalized state than the vegetable chyle in Marcet's experiments. Dr. Prout's results, for the most part, agree with those of Vauquelin and Marcet. The chyle was found to consist of a coagulum and a fluid part, which bore a general resemblance to the corresponding ingredients of the blood. In addition to these there was the oily or fatty matter, which appears, however, to have been in less quantity than in the animal chyle which was examined by Marcet. Dr. Prout likewise compared the chyle as produced from vegetable and from animal food, and found the former to contain more water and less albuminous matter, while the fibrous part and the salts were nearly the same in both; they are both said to have exhibited a trace of the oily matter; upon the whole he found less difference between the two kinds of chyle than had been noticed by Marcet. Dr. Prout has given us an interesting account of the successive changes which the chyle experiences in its passage along the vessels, having examined it when it first enters the lacteals, when it has arrived nearly at their termination, and when it is finally deposited in the thoracic duct. Its resemblance to the blood, as might be expected, was found to be increased in each of these successive stages of its progress.

The chyle, as it is formed or separated, is taken up

4 Ann. Phil. v. xiii. p. 22..5; see also Magendie, Phys. t. ii. p. 154.8. Magendie observes, that the opake white matter, which is observed in the serous part of chyle, is more abundant when the animal has used any considerable proportion of fat or oil in its diet; Ibid. p. 157.

by the lacteals, a set of vessels, the appropriate office of which is to convey this substance from the duodenum to the thoracic duct. Upon examining the contents of the different parts of the alimentary, canal, we observe that the chyle first makes its appearance soon after the chyme leaves the pylorus, that the greatest quantity of it appears to be formed at a short distance from this part, more especially, as it is said, near the orifice of the biliary duct, and that it gradually occurs in less and less quantity, as we pass along the small intestines, until it is no longer to be met with, and that, except in certain morbid states, where the contents are propelled with undue rapidity, no chyle is ever found beyond the small intestines.

The obvious and essential use of the large intestines is to carry off from the system the refuse matter, after the separation of the chyle from it; we may, however, suspect that in this, as in all other analogous instances, some secondary purpose of utility is served by them. This opinion is farther rendered probable by their anatomical structure, for besides their length, which although less than that of the small intestines, is still considerable, there is evidently a provision in them for retaining their contents, and preventing them from passing too rapidly through them. It is moreover observed, that there is an obvious change in the physical properties of the contents of the intestines from the time when they enter the cœcum until they arrive at the rectum. Although they no longer contain chyle, and are there

fore not furnished with lacteals, they have a number of lymphatic vessels connected with them, which absorb the more fluid parts of the fæces, and thus extract from them what may ultimately contribute to nutrition. That this is the case is rendered pro'bable by the effect of nutritive matter injected into the rectum, which, in cases of mechanical obstructions of the œsophagus, when food cannot be received into the stomach, has supported life for a certain length of time, proving the capacity of the organs to extract any portion of nutriment which may be mixed with their contents. Probably, however, the most important object to be gained by the structure of the large intestines, is to retain, for a certain length of time, the fæcal matter, which is gradually transmitted to them by the upper part of the canal, and to allow it to be evacuated at certain intervals only; a temporary detention of the contents being thus rendered necessary, advantage was taken of this circumstance to produce other beneficial effects in the system.3

5 Sommering, Corp. Hum. Fab. t. vi. p. 334.. 8. § 241. In the paper of Dr. Prout's, to which I have referred above, we have a series of very interesting observations on the successive changes which the alimentary mass experiences in its progress along the intestinal canal, both in different animals, and in the same kind of animal, when fed upon different kinds of food. It appears, as a general principle, that the process of digestion is more complete when animal food is employed, but we find that, in most cases, the fluids of the intestines continue to coagulate milk, even as low down as the rectum; Ann. Phil, v. xiii. p.-15 ..22. I have already offered some observations upon the hypothesis of Sir Ev. Home, in p. 353.

There are two of the abdominal viscera, which, from their connexion with the stomach, have been generally supposed to be subservient to the process of digestion; the pancreas and the spleen. The former of these, both from its intimate structure, and from the nature of the secretion which it furnishes, appears to be very similar to the salivary glands, and its office has accordingly been supposed to be that of providing a quantity of fluid resembling the saliva, which contribute to the completion of the pro

may cess of chylification."

The structure and function of the spleen is more obscure, and they have given rise to many hypotheses and conjectures which appear to be altogether unfounded, wholly unsupported either by any well ascer tained facts, or by the analogies of the animal co nomy. We are indebted to Sir E. Home, for what he conceives to be a more consistent account of the nature and use of this organ. He supposes that the spleen serves as a reservoir or receptacle for any fluid that is received into the stomach, more than what is sufficient for the purposes of digestion; that this excess of fluid is not carried off by the intestines, but is transmitted directly to the spleen by the communicating vessels, and is lodged there until it is gradually removed, partly by the veins and partly by the absorbents. He

See Santorini's fig. 1, in tab. 13. also references in p.343.. 7 See Haller, El. Phys. lib. xxi.; also Sommering, t. vi. p. 149. et seq. where the various uses that have been assigned to the spleen by physiologists are enumerated; the author does not offer any opinion of his own upon the subject.