In addition to Lieberkulin's follicles or tubes, which exist in the whole of the smaller intestine, there are other glandular or secreting structures, imbedded iu the submiicous tissue of certain portions of the intestinal tract, Which require consideration. These are: 1. Brunner's glands, which occur only in the duodenum; 2. Solitary glands, which seem to occur in all parts of the intestine, both small and large; and 3. Peyer's glands, which are usually confined to the ileum.
Brunner's glands are most abundant at the pyloric end of the duodenum. In struct ure, they resemble the pancreas, their ultimate elements being bunches of vesicles, from which minute ducts arise, which coalesce and form larger ducts, through which the secretion is poured into the duodenum. It is believed that they secrete a fluid similar to the pancreatic juice. The solitary glands occur in all parts of the intestine, but are perhaps more numerous in the jejunum than elsewhere. Each gland is a simple mem branous flask-shaped vesicle, the neck corresponding to the surface of the intestine, while the rounded base lies in the submucous tissue. The neck presents no opening, and how the contents, which consist of nuclei and granular particles, are discharged into the intestine, is not clearly known. As we never see them larger than a mustard seed, we may presume that, on attaining that size, they burst. Peyer's glands (fig. 9 are apparently mere aggregations of solitary glands, forming oval patches in the ileum. These patches vary in size and number, being largest towards the emeum, where their long diameter sometimes measures 3 or 4 in., and smallest towards the jejunum; while their number varies from 15 to 20, or even more. Nothing certain is known regarding the uses of these solitary or aggregated glands; but as they are largest during the digest ive process, we must. infer that they are in some way connected with that function. Possibly the peculiar odor of the faeces may be due to their secretion. In typhoid or enteric fever, and in plaids's, these glands become ulcerated, which probably occasions the diarrhea so common in these diseases.
Brunner's glands are much more developed in the herbivora than in the carnivore; Peyer's, on the other hand, are most developed in the latter.
We have endeavored, in the preceding sentences, to give the reader some idea of the complicated structure of the mucous and submucous coat of the small intestines; we now proceed to notice the chief uses of the muscular coat of the intestine. This coat, as has been already mentioned, consists of two layers of muscular fibers—namely, circular and longitudinal fibers, of which the former lie next to the submucous coat. The peri staltic or vermicular action by which the substances which enter the duodenum from the stomach are moved onwards, is due to this muscular coat. A person who has once seen the abdomen of an animal laid open immediately after death, will have a better idea of the nature of this movement than can be afforded by any description. It commences about the pyloric third of the stomach, from whence successive wave-like movements are propagated through the entire length of the intestinal canal. It is the
rapid succession of these alternate contractions and relaxations that impels the intestinal contents onwards, and occasion those movements which, from their resemblance to the writhings of a worm, have been termed repacular. It is very probable that the rapidity of this movement varies in different individuals—those persons, for example, whose bowels act twice daily having a more rapid vermicular motion than those in whom the act of defecation occurs only once in the twenty-four hours.
We have now to consider the effects produced on the chyme by the different fluids with which it becomes mixed in the small intestine. These fluids are: 1. The bile; 2. The pancreatic juice; and, 3. The intestinal juice.
The bile (see BILE) is a faintly alkaline or neutral fluid, containing two essential con stituents, one of which is of a resinous nature, while the other is a pigment. The resin ous constituent is not precisely identical in aff kinds of bile, but it generally consists of a soda-salt whose acid is either glyco-cholic or tauro-cholic acid (a.v ,), or of a mixture of these salts. Strecker, to whom we are mainly indebted for our knowledge of the chemistry of the bile, states that in most mammals the resinous constituent merely differs in the varying proportions in which the tauroeholates and glycocholates are inter mixed, the former usually preponderating. According to Lehmann, the resinous con stituent amounts to at least 75 per cent of the solid residue. The bile-pigment occurs in the bile of different animals under two forms—namely, as a brown and as a green pigment, the latter probably only differing from the former in being mere highly oxi dized. There has never been a case in which physiologists have had an opportunity of directly observing the quantity of bile that is secreted by the human subject, and all our information on this subject is derived from observations on animals, in which the ductus choledocleus cornM21111:8 (see LIN'En) has been tied, and a fistulous opening established into the gall-bladder. If the same proportion of bile to bodily weight holds good in man as in the dog, a man weighing ten stone would secrete daily about five pounds of bile. All observers agree, that the amount of the biliary secretion varies directly with the quantity of food; and as animals with biliary fistula' (in whom all the bile escapes externally, instead of making its way into the duodenum) usually have voracious appe tites, experiments on thiii point are easily made. There is great discrepancy Of opinion as to how soon after a meal the bile flows most abundantly into the intestine. Acco•d big to litilliker and Muller, whose experiments were made on dogs fed only once a day, very little bile is secreted in the first and second hour after a meal, more in the third, fourth, and fifth; the maximum being sometimes attained in the fifth, sometimes not till the eighth hour.