PROTEIN AND CIRCULATION 79 



only a fraction of that of the free amino acids. These 

 considerations, and the self-evident wasting of starved 

 tissues, point strongly to autolysis as the main source 

 of the free amino acids in the fasting body." 



"The failure to increase the free amino acid content 

 of the tissues by high protein feeding indicates, 

 furthermore, that when nitrogen is retained in the 

 organism it is not to an appreciable extent, as stored 

 digestion products, but rather as body protein." 



These results, and the consequent inference from 

 them, have made void all the older theories of metab- 

 olism and it is becoming more and more evident that 

 in any consideration of protein transformations within 

 the organism in health or in disease amino acids are 

 the substances which demand attention. This is the 

 age of amino acid metabolism and at present the inves- 

 tigations are being narrowed down to the point of the 

 determination of what actually occurs with the indi- 

 vidual amino acids and what special role in nutrition 

 each may play. 



REFERENCES TO LITERATURE 



Abderhalden: Zeitschrift fur physiologische Chemie. 1913, 

 88, p. 478. [Amino acids in blood.] 



Abderhalden: Text Book of Physiological Chemistry. 1914. 

 [Enzymes in blood.] 



Cathcart: The Physiology of Protein Metabolism. 1912. 



