The formation of Chyle, or the fluid which is the immediate and exclusive source of nutriment to the system, takes place in the intestinal tube, into which the chyme prepared by the stomach is received, and where farther chemical changes are effected in its composition. The mode in which the conversion of chyme into chyle is accomplished, and indeed the exact nature of the changes themselves, being, as yet, very imperfectly known, it is consequently impossible to trace distinctly the correspondence which, in all cases, undoubtedly exists between the objects, to be answered, and the means employed for their attainment. No doubt can be entertained of the importance of the functions that are performed by structures so large and so complicated as are those composing the alimentary canal, and its various appendages. We plainly perceive that provision is made in the interior of that canal, for subjecting its contents to the action, first, of an extensive vascular and nervous surface; and secondly, of various fluid secretions, derived from different sources, and exercising powerful chemical agencies on the digested aliment; that a muscular power is supplied, by means of the layers of circular and longitudinal fibres, contained between the outer and inner coats of the intestine, for exerting a certain pressure on their contents, and for propelling them forwards by a succession of contractions, which constitutes what is termed their peristaltic motion; and lastly, that contrivances are at the same time resorted to for retarding the progress of the aliment in its passage along the canal, so that it may receive the full action of these several agents, and yield the utmost quantity of nutriment it is capable of affording.