PROTEIN AND CIRCULATION 75 



to prove absorption and the existence in the blood of 

 certain amino acids but failed to detect these sub- 

 stances when experiments were carried out on the 

 intact animal. 



By the elaboration of new methods, Folin and Denis 

 and Van Slyke and Meyer have been able to prove the 

 entrance of amino acids into the blood stream. Later, 

 Abderhalden, the chief opponent of the idea of amino 

 acid absorption, was successful in isolating from the 

 blood several of the individual amino acids by the 

 employment of great volumes of blood. The absorp- 

 tion of protein in the form of amino acids having thus 

 been established the question next arises what becomes 

 of them? It was soon proved that there was a rapid 

 disappearance of amino acids from the circulation and 

 this fact made pertinent the queries : "Are they decom- 

 posed in the blood: are they chemically incorporated 

 into the complex molecules of the tissue proteins; or 

 are they merely absorbed by the tissues in general, or 

 by certain tissues in particular, without undergoing 

 any immediate change?" These questions have been 

 fully answered by Van Slyke and Meyer in experi- 

 ments designed to follow the fate of the amino acids 

 after absorption. It was found that the amino acids 

 are absorbed by the tissues without undergoing any 

 immediate chemical change. This absorption though 

 rapid is never complete, the blood always containing 

 a small quantity of amino acids. It would appear 

 from this that there is an equilibrium between the 

 amino acids of the blood and of the tissues. The way 



