CHAPTER XVII. 



THE ALIMENTARY TRACT AS AN ABSORPTIVE SYSTEM. 



(Concluded). 



10. The Absorption of Proteins. Since the proteins, un- 

 like the salts and water, and like the fats and certain carbo- 

 hydrates, suffer profound changes in their passage through 

 the alimentary tract, the question arises first of all, Are the 

 proteins absorbed entirely or in part as such, or do they first 

 suffer a decomposition into simpler substances before they 

 pass through the absorbing wall of the intestinal tract? 



Physico-chemical reasons indicate that the proteins are not 

 absorbed as such, or only in very small amounts, for belong- 

 ing as they do to the general class of the colloids they are not 

 able, practically speaking, to diffuse through a colloidal mem- 

 brane such as the alimentary tract presents. Experimental 

 facts agree entirely with this reasoning. As FRIEDLANDER'S * 

 experiments have shown, acid-albumin does not disappear 

 when introduced into a well-washed loop of intestine. In 

 opposition to this are the experimental results of most other 

 observers. BRUCKE, VOIT, BAUER, CZERNY, LATSCHENBERGER, 

 NEUMEISTER, and MUNK all believe that no inconsiderable 

 amounts of such substances as egg-albumin, myosin, blood- 

 serum, and acid-albumin can be absorbed as such from care- 

 fully cleaned loops of intestine in the course of one to four 

 hours. The disappearance of even 10 or 20 percent of the 

 protein introduced in this way does not prove necessarily 

 that it was absorbed in the " native " state. The fact that the 



1 FRIEDLANDER, Zeitschr. f. Biol., 1896 XXXIII, p. 274. 



299 



