THE METABOLISM OF PROTEIN 



607 



a marked increase, becoming doubled or more; and a similar result has 

 been obtained by placing pure amino acids in the small intestine. After 

 10 grams of alanine, for example, the amino nitrogen of the mesenteric 

 blood rose from 3.7 to 6.3 mg. per cent.* 



In the Tissues. After entering the circulation, the amino acid very 

 quickly disappear from it again. This has been demonstrated by ob- 

 serving the amount of amino acids in the blood after intravenously 

 injecting a solution of amino acid into an anesthetized animal. After 

 injecting 12 gm. of alanine into the vein of a dog, 90 per cent was found 



Fig. 186. Vividiffusion apparatus of J. J. Abel.* 



to have disappeared from the circulation within five minutes. The ques- 

 tion is, What becomes of the amino acids that rapidly disappear? Are 

 they decomposed in the blood, or do they become absorbed by the tis- 

 sues? This problem has been attacked by analyzing portions of various 

 organs and tissues removed before and some time after the injection 

 into an animal of amino acid solutions. In the case of the muscles it 

 has been found that the amino-acid content increases until from 60 to 

 80 mg. per cent of amino acid has accumulated. Beyond this point, 

 however, the muscles do not seem to be able to take up any more amino 

 acid. The capacity of the intestinal organs, however, is more elastic; 



"This is a convenient way of stating per 100 c.c. of blood. 



