DIGESTION. 24r5 DIGESTION. that function. Possibly the peculiar odor of the faeces may be due to their secretion. In typhoid or enteric fever, and in phthisis, these glands become ulcerated, which probably occa- sioDs the diarrluva so common in these diseases. Brunner's glands are much more developed in the hcrbivora than in the carnivora ; Peyer's, on the other hand, are most developed in the latter. We have endeavored, in the preceding sen- tences, to give the reader some idea of the com- plicated structure of the mucous and subnmeous 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 men- tioned, consists of two layers of muscular fibres — namely, circular qnd longitudinal fibres, of which the former lie next to the submucous coat. The peristaltic or vermicular action, by which the substances which enter the duodenum from the stomach are moved onward, is due to this muscular eoat. 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 afl'orded by any description. It commences about the pyloric third of the stomach, whence successive wave- like movements are iiropagatcd through the entire length of the intestinal canal. It is the rapid succession of these alternate contractions and relaxations that impels the intestinal con- tents onward, and occasions those movements which, from their resemblance to the writhings of a worm, have been termed vermicular. It is very probable that the rapidity of this movement varies in different individuals — those persons, for example, whose bowels act twice daily hav- ing 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 eflfects 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 (q.v.) is a faintly alkaline or neutral fluid containing two essential constituents, one of which is of a resinous nature, while the other is a pigment. The resinous constituent is not pre- cisely identical in all kinds of bile, but it gen- erally consists of a soda .salt whose acid is either glycocholic or tauroeholic acid, 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 resin- ous constituent merely differs in the varying proportions in which the taurocholates and gly- eocholates are intermixed, the former usually preponderating. According to Lehmann, the resinous constituent amounts to at least 75 per cent, of the solid residue. The bile pigment oc- curs in the bile of different animals under two forms — namely, as a brown and as a green pig- ment, the latter probably onlv differing from the former in being more highty oxidized. 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 common bile-duct (see Liver) 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 a.s in the dog, a man weighing 140 pounds would secrete daily about live 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 fistulie (in whom all the bile escapes externally, instead of making its way into the duodenum) usually have voracious appetites, experiments on this i)oint are easily made. There is great discrepancy of opinion as to how soon after a meal the bile flows most abundantly into the intestine. According to Kiillikcr and Jliiller, 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. Numerous and somewhat discrepant views have at different times been advanced regarding the functions of this fluid; we shall liero notice only those functions which are connected with diges- tion. One use that has . been ascribed to it is to neutralize in the small intestine the acid chyme «hich emerges from the stomach. But the bile can contribute little or nothing to the neu- tralization of the free acid, because, in the first place, the bile is very slightly alkaline, and often perfectly neutral: and, secondly, because the chyme in the intestine is still acid after the ad- mixture of the bile. Again, the bile has been as- serted to possess a special solvent action on the chyme; but none of the ordinary constituents of the latter seem to be essentially changed, even «hen digested for a long time w-ith fresh bile. Again, much importance has been attached to the antiseptic action of the bile on the contents of the intestinal canal, in favor of which view it is alleged that when no bile is poured into the in- testine the fa-ces have a putrid odor, as is some- times observed in patients with jaundice, and as was noticed by Frerichs in animals in which the common bile-duct had been tied. Another use that has been assigned to the bile is that it exerts a stimulating action on the intestinal w-alls. and thus acts as a natural purgative; and in support of this view it may be mentioned that jaimdice (in which the bile does not flow into the intes- tine) is often accompanied by extreme constipa- tion, and that purified ox-gall, taken either in the form of pill or enema, produces an undoubted purgative action. But the main use of the bile seems to be to promote the digestion of fatty matters; and it accomplishes this end not so much by any solvent chemical action on the fats (which at most is extremely slight), as by a peculiar physical action both on the fats and on the intestinal walls, disintegrating the former and impressing on the latter (by moistening the villi) a peculiar condition which singularly fa- cilitates the absorption of fatty matters. Thi? view is fully confirmed both by direct experi- ments out of the body and by comparing the rela- tive qualities of fat that are retained in the body and applied to the purposes of life by animals with biliary fistulous openings and by healthy animals. The pancreatic fluid which is poured into the duodenum at the .same spot with the bile (see Fig. 1 ) is a colorless, clear, somewhat viscid and ropy fluid, devoid of any special odor, and exhibiting a strong alkaline reaction. This fluid, as yielded by different dogs with permanent fistulous openings, varies considerably in cheni-
