12 THE PHYSIOLOGY OF PROTEIN METABOLISM 



Absorption of Undigested Protein from the Intestine. 



The question as to whether the completely undigested protein can 

 be absorbed must also be considered. Magnus- Levy has suggested that 

 the body may absorb from the intestine a sufficient amount of unaltered 

 protein for purposes of repair of tissue, but that the greater part of the 

 protein is broken down to simple nuclei, which are simply burnt up 

 without playing any part in the tissue metabolism. That the body can 

 absorb protein in the natural form has long been known. Voit and 

 Bauer (408) showed that the absorption of undigested proteins such as 

 serum and uncoagulated egg albumin could take place, and their re- 

 sults have been extended and amplified by Heidenhain (180), Fried- 

 lander (149), Waymouth Reid (416), and others. It is not maintained, 

 however, that this is the way in which most of the absorption takes 

 place. Ascoli and Vigano (55), using the biological precipitin test, 

 have stated that they were able to demonstrate that part of the protein 

 was taken up unchanged. Abderhalden, Funk and London (41), under 

 much better conditions than Ascoli, and also using the biological 

 method, were quite unable to obtain any reaction. In all these ex- 

 periments the protein was introduced into the intestine in excessive 

 amount. This absorption, such as it is, would appear to be dependent 

 to some extent on an increased permeability of the intestinal wall, 

 such as is found in the young. It is also dependent to a certain 

 extent on the presence of water or salt solution. Friedlander (149), 

 for instance, has shown that, if all the water or salt solution be absorbed, 

 the absorption of the proteins to all intents and purposes comes to a 

 standstill. Naturally doubts have been thrown on this form of 

 absorption. It has been suggested that the intestinal digestion had 

 not really been suspended, although the intestine previous to the intro- 

 duction of the protein solution had been thoroughly washed out, i.e. 

 that a certain amount of pancreatic juice had been left which brought 

 about a solution of the protein, and thus a natural absorption. This 

 objection is not valid, however, as the protein was rapidly absorbed, 

 and further the amount of enzyme which could have been present 

 must have been small and its activity on native protein slight. For 

 example, the figures quoted both by Heidenhain (180) and by Way- 

 mouth Reid (416) show that the intestine can deal with large amounts 

 of protein in a very short period of time. 



Omi (311) has made a curious observation in connexion with the 

 absorption of native protein. He found that dog serum is readily ab- 

 sorbed from the dog's intestine, but that if horse or ox serum be em- 



