342 A MANUAL OF PHYSIOLOGY. 



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 pro- 

 teins, 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, 07 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 con- 

 tented 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 concen- 

 tration, 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 neutralizing 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. 328). 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 maybe 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 reaction (ammonia, mono-amino acids, 

 hexone bases, etc.). It destroys the diphtheria toxin, which 



