able to modify it only by varying, through the medium of the stomach, the elements out of which chyle is to be formed and the mode in which they shall be digested, is a proof that, practically speaking, it is chiefly the laws or conditions of stomachic digestion which are intended to regulate our conduct; and that, in obeying them, we in reality obey also those of intestinal digestion.

The organs concerned in chylification are the duodenum, the liver, and the pancreas; but in order to avoid repetition, I shall, in describing the first, notice also the remainder of the intestine.

The intestine or intestinal canal, as represented in the subjoined figure, begins at the pyloric orifice of the stomach P, and after many windings and turnings, called convolutions (from the Latin word convolutus, rolled or folded together), terminates in the rectum or straight gut Y, at the external orifice called the anus. Although continuous throughout its whole extent, the intestinal tube is nevertheless divided by anatomists into six portions, to each of which a different name is assigned: the distinction between some of these is more nominal than real, but it still continues to be made on account of its convenience.

The first grand division is into the small and great intestines; the former beginning at the stomach, including all the convolutions marked R S S S S,—and the latter beginning at T, where the small intestine terminates, and including the large gut UUUUX Y Y, which surrounds, and is partly hidden by, the other bowels.

The small intestines, again, are subdivided into three

portions, the duodenum, the jejunum, and the ileum; and the larger, in like manner, into three portions-the caput cæcum or simply the cacum, the colon, and the

rectum. Of the whole length, the small intestines constitute by much the greater part, and they differ somewhat from the larger in function as well as in magnitude.

In structure, the intestines exhibit a great analogy with the stomach. They consist, in common with it, of three coats or layers of membrane; the outer or peritoneal,— the middle or muscular,-and the internal, mucous, or villous.

The peritoneal coat is the white, firm, smooth, shining, and moist membrane, seen on the outside of the intestine on opening the cavity of the abdomen. It serves both as a support and as a medium of attachment to fix the intestine in its place. By its smooth, soft, and lubri cated surface, it admits readily of the change of place among the bowels necessarily produced by respiration, exercise, and even by different degrees of distention of the bowels themselves. Every time we breathe, an undulating motion is communicated to the whole intestines, which facilitates their action, but which could not take place unless they were capable of gliding easily and freely over each other. The peritoneal coat, being strong, extensible, and elastic, is very useful also as a support to the other coats.

The peritoneal coat, after forming the outer covering of the intestine, represented by the dotted line round the circle I in the figure on next page, is continued from it in the form of a double membrane (represented by the two dotted lines) towards the spine S, to which it is first firmly attached by cellular substance; after which the folds again separate, each being continued or reflected, as it is called, over the whole inner substance of the cavity

of the abdomen in the course shewn by the dotted line, the figure itself representing a transverse section of the abdomen. By this arrangement two important objects

I

AP

M

AP

are attained. First, the abdominal peritoneum AP forms a soft lubricated surface, corresponding to that of the bowels themselves; and, secondly, a firm point of attachment for the bowels is secured, by which they may be supported in their proper places, and at the same time admit of some change of position. The floating portion of the peritoneum M, by which the attachment is effected, is called the mesentery (from μeños, mesos, the middle, and evtɛgov, enteron, intestine). But the intestinal canal being so much longer than the portion of the spine, to which the mesentery is attached, the latter is necessarily disposed in folds converging towards the spine, something like the folds of a fan converging towards its narrow end. In this way, the mesentery, besides serving as a support to the gut, serves also to receive and afford protection to the numerous vessels, nerves, and lacteals which are copiously ramified on every portion, particularly of the small intestines. This feature, however,

will be better understood by inspecting the wood-cut on page 163, representing a portion of the bowel II, as attached to the spines by the mesentery MM, along which the absorbent vessels or lacteals LL are seen to pass from the gut towards the thoracic duct TD.

The portion of peritoneum by which the small intestines are fixed to the spine, constitutes what is properly called the mesentery. That portion by which the larger bowel is attached is called the mesocolon, from its enclosing the colon; but in other respects the membrane presents no difference.

The muscular coat is composed principally of transverse and longitudinal fibres, and its sole object here, as elsewhere, is to effect motion. By the alternate contraction of the two kinds of fibres, the contents of the gut are gradually propelled in a downward direction, just as we see a motion propagated from one end of a worm to the other; and hence it is sometimes called the vermicular or worm-like motion (from vermis, a worm). Some nauseating substances, such as emetics, have the power of inverting the order of the muscular contractions, and directing the contents upwards instead of downwards-whence vomiting ultimately arises. Other substances, again, have the property of exciting the natural action to a higher degree, and consequently propelling the contents faster downwards-in other words, of purging. Rhubarb, aloes, and similar laxatives, especially when combined with tonics, act in this way, and are consequently best adapted for obviating the kind of costiveness which arises from imperfect intestinal contraction. In a natural mode of life,