The food then in the stomach is in part dissolved by the saliva and fluids of the organ; broken down by fermentation, and, by the latter process, in part ani-malised. In this state it is carried into the duodenum, a portion of the intestine, for the reasons assigned, capable of a considerable dilatation. It is here exposed to the influence of bile, a fluid, as we have seen, which has almost undergone a second circulation, without being exposed to the air; or, what is of more consequence, without being mixed with fresh,animal matter. It is evidently more animalized than any other fluid of the body; and, by its union with the chyme, new combinations take place, which have not yet been accurately observed. Our food, we have said, consists of gelatine, oil, and sugar. These substances are the chief component parts of the chyle. When the vegetable substances are then broken down, we want little more than their separation from the other ingredients, which may be probably effected by the bile, and perhaps the combination of a small portion of azote. Fourcroy supposes that the alkali, and other saline parts of the bile, are combined with the chyle to attenuate it, and that its resin is discharged with the excrements. We should rather suspect that the alkali itself was decomposed, and its azote only combined with the chyle. We certainly find the resin of the bile in the excrementitious part of the contents of the intestines. The pancreatic fluid is here also added; and we have reason to suppose that it dilutes the chyle, while, as an animal fluid, it contributes to the necessary change.
The next portion of the intestine is called jejunum. It is distinguished by no peculiar structure, and differs from the rest of the small intestines by being frequently found empty. The only consequence to be drawn from this is, that, in the duodenum, digestion is perfected, and no longer delay is required. As the food, however, proceeds, the process of animalisation appears to go on; and, from the large intestines, the chyle seems to differ in some respects, at least in colour, from that which is carried from the ilium.
In the progress of the alimentary fluid through the lacteals, we find it often conveyed into glands, called lymphatic, or conglobate. It is here apparently deposited into cells, and mixed still more intimately with animal fluids, from whence it is absorbed by other lacteals, which apparently possess some elective power. Partly for the purpose of a more complete animalisation, and partly to prevent any noxious substance from contaminating the vital fluid, these glands are seemingly interposed. We see an equal anxiety for each purpose in the' further provisions. The new aliment is mixed in the thoracic duct with the lymph, absorbed from every cavity, and, even after every precaution, conveyed almost by drops into the blood. It is thus carried gradually to the heart and the lungs, where the last process takes place.
We are now well acquainted with the changes which are produced in this part of the animal system. Atmospheric air is absorbed, and its oxygen, in part, uniting with the blood, gives it a florid hue; and, in part, combining with the carbone, separates it in the form of carbonic acid gas. It is, indeed, doubtful whether any oxygen remains; and whether the separation of the carbone alone may not produce the sensible changes attributed to the oxygen. Our vegetable food, by the gradual admixture of fluids more highly animalised, has now become near to our own nature, but it is still not azotic. This last principle seems to be supplied by the air, from whence azote is very probably absorbed. The experiments by which this is ascertained are not before the public; but those communicated to us render it highly probable.
It may be said, that, though the bile be obstructed, digestion goes on. It does so; but imperfectly, and the body is emaciated, the strength diminished, and atrophy is the consequence. There is some doubt whether any considerable portion of nourishment is, in such cases, conveyed through the lacteals, and whether the body is not supported by absorption from the adipose membrane, It will be obvious, however, that some nourishment must still be obtained; for the bile, returned to the blood, is discharged by every excretory duct, and, among the rest, by the mucous glands and the pancreas. A small portion, therefore, finds its way to the digestive organs; and those who have remarked with how inconsiderable a degree of nutriment the body is sometimes supported, will not be surprised at the effect of the pittance it must in this way receive.
Another objection will be suggested, by the almost total obstruction of the mesenteric glands in some cases of scrofula. Yet, on minute observation, it will appear that every lacteal does not press through a gland. Sometimes it creeps over the surface to immerge in the following; and sometimes it seems cautiously to avoid every body of this kind interposed.
The "play of affinities,"which takes place on the mixture of the bile, is not yet understood. It is certainly considerable; for we sometimes find the benzoic acid in the excrements of herbivorous animals, and sometimes the phosphoric. The former we have reason to believe, from some late experiments, to be a product, whose basis is the vegetable acid; and the latter we have begun to detect in its disguise, and to trace its source in grain. These subjects will soon be more clearly elucidated. Whether produced in the intestines, in the different cavities, or in the circulating system, is yet uncertain; but the phosphoric acid and the ammonia are the creatures of the animal economy, produced by the new combinations constantly taking place.'
The red globules of the blood, though evidently derived from the nutriment, resemble so little every part of it, except the oil, that we must profess ourselves ignorant of their source. They are not oily; and though we lose the oil that makes a part of our food, and which is discoverable in the chyle, we can scarcely think that it forms this singular portion of our fluids. It is apparently decomposed, and affords the hydrogen, which is a component part of the animal economy. When we reflect, however, on the other hand, that we have scarcely any instance of globules swimming, unmixed, in a watery fluid, without being oleaginous; that oil affords a very solid, substantial nutriment; and that the red globules are numerous and vivid, in proportion to the strength of the constitution; we have some reason to suppose that they derive, in part, their origin from this source, though (hanged in their chemical properties. The application of these newly formed fluids must be the subject of fu-lure consideration. Sec Nutrition.