316 A MANUAL OF PHYSIOLOGY 



a loop of intestine from the rest by two transverse cuts, the abdomen 

 having been opened in the linea alba. The continuity of the digestive 

 tube is restored by stitching the portion below the isolated loop to 

 the part above it ; one end of the loop is sutured to the lips of the 

 wound in the linea alba, and the other being ligatured, the whole 

 forms a sort of test-tube opening externally (Thiry's fistula). Or 

 both ends are made to open through the abdominal wound (Vella's 

 fistula). Another method is to make a single opening in the intestine, 

 and by means of two indiarubber balls, one of which is pushed down, 

 and the other up through the opening, and which are afterwards 

 inflated, to block off a piece of the gut from communication with the 

 rest. The intestinal juice so obtained is a thin yellowish liquid of 

 alkaline reaction. Its specific gravity is about 1010. It contains a 

 small amount of proteids, and about the same proportion of inorganic 

 salts as most of the liquids and solids of the body, namely, 7 or '8 

 per cent. ; but its composition seems to be far from constant. It has 

 been credited with various digestive powers ; in fact, according to 

 one or two enthusiastic observers, it would almost seem to sum 

 up in itself the actions of all the other digestive juices, and to possess 

 besides a peculiar activity of its own. But we need not hesitate 

 to say that in the work of digestion it plays a subordinate part. 

 The sodium carbonate, in which it is exceedingly rich, will form 

 soaps with fatty acids produced by the action of the pancreatic 

 juice or of the fat-splitting bacteria in which the intestine abounds, 

 and thus aid in the digestion of fats. That a great deal of fat 

 may be split up in the alimentary canal in the absence both of bile 

 and pancreatic juice is well ascertained. The alkali of the succus 

 entericus will at the same time check the growing acidity of the 

 intestinal contents. A ferment called invertin which is not intro- 

 duced with the food or formed by bacterial action as has been sug- 

 gested, since it occurs in the aseptic intestine of the new-born child 

 changes cane sugar into a mixture of dextrose and levulose ; some 

 maltose may be changed into dextrose. Here, however, the catalogue 

 of the powers of the succus entericus ceases ; on proteids and starch 

 it has little or no action. But the secretion of Brunner's glands in 

 the duodenum, which resemble in structure the pyloric glands of the 

 stomach, digests coagulated albumin, although its proteolytic powers 

 are feebler than those of the pancreatic juice. And in all the young 

 mammals hitherto investigated, including the new-born child, the 

 small intestine throughout its whole extent contains a ferment which 

 has the property of forming lactic acid from lactose. This is present 

 also in some adult mammals, but it has not been shown that it is a 

 constituent of the pure intestinal juice. 



Having now finished our review of the chemistry of the 

 digestive juices, our next task is to describe what is known 

 as to their secretion the nature of the cells by which it is 

 effected and their histological appearance in activity and 

 repose, and the manner in which it is called forth and 

 controlled. 



