ALIMENTARY TRACT AS AN ABSORPTIVE SYSTEM. 301 



tease (erepsin). The arguments which point in this direction 

 are the following: The proteoses still stand close to the so- 

 called " typical" colloids, and their absorption as such is 

 open to the same objections from a physico-chemical stand- 

 point which were raised against the albumins from which 

 they are derived. The same holds true of many of the 

 peptones (in KUHNE'S sense), though some of them approxi- 

 mate the crystalloids in their physical behavior. In any 

 case, both classes of substances -are readily decomposed under 

 the conditions existing in the body. As agencies bringing 

 about such a decomposition we have the already-mentioned 

 proteolytic ferments. Recent work indicates that acid-pro- 

 teinase approximates at least qualitatively the proteolytic 

 activity of alkali-proteinase, and in protease we have a newly 

 discovered ferment which seems to be most energetic in break- 

 ing down proteoses and peptones into the simple crystalline 

 products which have long been considered characteristic of 

 the activity of alkali-proteinase (trypsin). Finally, if the 

 proteins are really broken up into simple crystalline sub- 

 stances before being absorbed it ought to be possible to find 

 them in the alimentary contents. This has been done by 

 KUTSCHER and SEEMANN, who succeeded in obtaining leucin, 

 tyrosin, and lysin from the intestinal contents of the dog. 

 The amount which they obtained was not large, and this is 

 often taken as an argument to show that not all or even a 

 large part of the protein of a meal is split as far as the mono- 

 and diamino-acids. The objection is perhaps scarcely a 

 valid one, for not only are these substances readily diffusible 

 so that a collection of a considerable amount is rendered 

 well-nigh impossible, but all the proteolytic change does not 

 occur in the lumen of the gut; part takes place in the wall 

 of the intestine, where protease (erepsin) is present in large 

 amounts and into which at least some of the peptones diffuse 

 easily. All these facts seem to indicate, therefore, that the 

 proteins are absorbed, at least in the main, in the form of 

 the simplest digestion products. 



