In proportion as the chyme is formed and expelled from the stomach, it is received into the duodenum, where it probably undergoes some farther change even before arriving at the entrance of the biliary and pancreatic ducts. From the numerous folds or wrinkles which line the inner surface of the duodenum and impede the motion of its contents, and also from the intestine itself being more fixed down, and less subjected to the influence of the movements of respiration, the progress of the chyme along its surface is very slow. Every particle of chyme is thus allowed to receive its share of the bile and pancreatic juice as it proceeds on its course, and time is afforded for the requisite changes taking place. By simply stating that, in the duodenum, the chyme becomes mixed with the two fluids just mentioned, and that the result is its separation into a fluid, milky, and nutritive portion, named _chyle_, which is absorbed by the lacteals, and a darker yellow-coloured thickish mass which remains in the bowel, we communicate to the reader almost every thing that is known on the subject. Theories and conjectures could be added, but scarcely any facts of a very positive nature. * * * * * The remainder of the small intestine, namely, the _jejunum_ (from _jejunus_, fasting or hungry, because it is generally empty) and the _ileum_ (from ειλεω, _eilio_, I twist or turn about), marked RSSSS in the cut on p. 155, are merely continuations of the duodenum, and have precisely the same number of coats and the same general structure. Their inner surface presents the same kind of folds or _rugæ_, whereby the extent of the mucous membrane is increased, and ample space given for the ramifications of bloodvessels and the origin of the absorbents by which the chyle is sucked up and carried into the system. _Exhalation_ or _exudation_ also goes on from their surface, and, in bowel-complaints, often becomes so excessive as in a few days to reduce the patient to the extremity of emaciation and weakness. As the contents of the jejunum and ileum advance, the proportion of chyle in them becomes smaller and smaller, and the residual matter becomes more and more consistent, yellow, and fetid--approaching, in short, to the ordinary appearance of excrement when expelled from the body. In accordance with these changes, the number of absorbent vessels, and the distinctness of the villous folds, gradually diminish as we proceed downwards, till, on arriving at the termination of the ileum in the colon or great gut, they altogether disappear, and the contents assume the colour, smell, and appearance, by which excrement or feculent matter is characterized.