78 THE AMINO ACIDS 



material. In either case the supply would be depleted 

 if not renewed from the food. 2. The amino acids 

 are merely intermediate steps in both the construction 

 and breakdown of the tissue proteins. In this case they 

 could originate, not only from absorbed food products, 

 but also from autolyzed tissue protein: starvation 

 would not result in a disappearance of the amino acid 

 supply of the tissues, and might even increase it. To 

 determine the correctness of one or the other of these 

 hypotheses the authors mentioned above analyzed the 

 tissues of animals in various states of nutrition. The 

 results are in harmony with the second hypothesis, for 

 free amino acids of the tissues tend to increase in 

 starvation rather than to disappear. The investigators 

 have summarized their views regarding this in the fol- 

 io-vying words : "The amino acids appear, therefore, to 

 be intermediate steps, not only in the synthesis, but in 

 the breaking down of body proteins. Otherwise, in 

 order to explain their maintenance in the tissues during 

 starvation, one would be forced, contrary to the con- 

 clusions of all experimental work on the subject, to 

 assume that they are inert substances lying unchanged 

 for long periods, even when most urgently needed to 

 build tissue or supply energy. The maintenance of 

 the amino acid supply by synthesis, from ammonia and 

 the products of fats or carbohydrates, seems excluded. 

 The supply of raw material in the form of fat and 

 carbohydrates nearly disappears during starvation, and 

 the ammonia could originate only from broken-down 

 protein, as the normal store of ammonia nitrogen is 



