THE CHEMISTRY OF THE DIGESTIVE JUICES 371 



secretions which enter the higher portions of the alimentary canal 

 (gastric juice, pancreatic juice, and bile). The intestinal juice so 

 obtained is a thin yellowish liquid of alkaline reaction, generally 

 somewhat turbid from the presence of a certain number of leucocytes 

 and epithelial cells. Its specific gravity is about 1010, the total 

 solids about 1-5 per cent. It contains a small amount of proteins, 

 including serum albumin and serum globulin, and about the same 

 proportion of inorganic salts as most of the liquids and solids of the 

 body, namely, 0-7 or 0-8 per cent., chiefly sodium carbonate and 

 sodium chloride; but, like the other digestive liquids, it is adapted 

 to the nature of the food, and therefore its composition is not quite 

 constant. Like bile, intestinal juice acts but feebly on the food 

 substances by itself, and if we contented ourselves with examining 

 the pure and isolated secretion, we should greatly underestimate its 

 importance. The sodium carbonate, in which it is relatively rich, 

 will, to be sure, 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. A lipase, 

 feebler than that of the pancreatic juice, or present in smaller con- 

 centration, is also a constituent of the succus entericus. 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 must at the same time aid in neutraliz- 

 ing the original acidity of the chyme, and in preserving the proper 

 reaction of the intestinal contents. A ferment called invertase, or 

 sucrase which is not introduced with the food or formed by bacterial 

 action as has been suggested, since it occurs in the aseptic intestine 

 of the new-born child will invert cane-sugar. The ferments maltase 

 and lactase will cause a corresponding change in maltose and lactose 

 (see footnote, p. 356). It is worthy of remark that these inverting 

 enzymes are present in the intestinal mucosa as well as in the 

 intestinal juice, and extracts of the mucosa are usually distinctly 

 more active than the juice itself. So that there is reason to believe 

 that hydrolysis of the disaccharides may take place both in the 

 lumen of the gut before absorption and in the wall of the gut during 

 absorption. Inverting enzymes appear in the intestine early in 

 embryonic life. Maltase is the most generally distributed of all 

 these enzymes, and it is found along with lactase in the intestine of 

 the embryo pig, while invertase is missing till after birth (Mendel). 

 On native proteins and starch the isolated succus entericus has little 

 or no action. But it contains a ferment, erepsin, which, although it 

 does not affect native proteins like serum- and egg-albumin (fibrin 

 and caseinogen may be slightly digested), exerts a powerful action 

 on the first products of protein hydrolysis, albumoses, and peptones, 

 breaking them up into bodies which no longer give the biuret re- 

 action (ammonia, mono-amino acids, hexone bases, etc.). It 



