24 THE PHYSIOLOGY OF PROTEIN METABOLISM 



digestion, he was unable to prove that there was any accumulation of 

 nitrogenous material. This is, of course, no proof that such a syn- 

 thesis does not take place, as it is possible, although highly improb- 

 able, that the synthetic product is very rapidly formed (constant 

 synthetic action) and just as rapidly removed. It does not, on the 

 other hand, support the immediate resynthesis hypothesis. Korosy 

 (225) carried out a large number of absorption experiments under 

 different conditions, using a method very similar to that followed by 

 Cathcart and Leathes. He pronounced, however, in favour of im- 

 mediate resynthesis, on the grounds that in dogs with their circulation 

 restricted to the intestine the non-precipitable nitrogen (by the tannic 

 acid method) in relation to the total nitrogen of the blood is not in- 

 creased after a protein meal in greater amount than that which is found 

 in fasting. He was unable to detect any free amino acids or proteoses 

 in the blood, and this he regarded as an additional argument for im- 

 mediate resynthesis. 



Cohnheim (96), on the other hand, produced some evidence which 

 distinctly favoured the view that the absorbed protein material travelled 

 in the blood in the form of amino acids. He carried out his experi- 

 ments on the intestine of the Octopus and the Eledone moschata. He 

 introduced solutions of peptone into the isolated gastro- intestinal tract 

 which he floated in oxygenated blood. Not only was he able to prove 

 that absorption took place, but that amino acids were absorbed, at any 

 rate under the conditions of his experiment, as he was able to isolate 

 from the blood at the conclusion of the experiment, which lasted 

 twenty hours, leucine, tyrosine, lysine, arginine and ammonia. When, 

 however, he carried out similar absorption experiments on the intact 

 animal, he was unable to detect these amino acids in the blood. 



The Nature of the Absorbed Material. 



Thus there is no direct evidence which definitely determines the 

 form in which the digestion products of protein reach and travel in 

 the blood. Wherein, it might be asked, lies the benefit of converting 

 the protein into simple products like the amino acids to have them 

 immediately after absorption takes place converted into a neutral pro- 

 tein. The complete breakdown in the gastro-intestinal tract probably 

 takes place either because the highly complex molecule is not readily 

 dealt with as such by the tissues or because certain amino acids, 

 as for example glutamic acid in gliadin, which are present in excess. 



