104 A. I. RINGER 



Until about ten years ago it was believed that the amino acids were 

 resynthesized into serum albumin and serum globulin while passing through 

 the cells of the intestinal wall, and that these two products constituted 

 the sole source from which all the body proteins were built up. The rea- 

 son for that view was that while amino acids could be found in the in- 

 testines, none could be discovered in the blood stream. But since Van 

 Slyke's introduction of his micro method for amino acid determination, 

 this view had to be abandoned. Amino acids were then found to be pres- 

 ent in the blood of fasting animals to the extent of 3 to 5 mg. per 100 c.c. 

 of blood, and after a meal of meat the figures rose to 10 and 11 mgs. 

 (calculated as amino acid nitrogen; Van Slyke, G. M. Meyer, 1913). 

 Similar results were also obtained by Abderhalden and Lampe, 1912, and 

 Folin and Denis, 1912 (a). 



The Fate of Absorbed Amino Acids in the Blood 



The amino acids, after they enter the blood stream, disappear 

 from it fairly rapidly. This we know from various sources. First from 

 the fact that, there is. but a very moderate rise in the amino acid nitrogen 

 content of the blood during the height of digestion of a protein meal. 

 Second from the results of the Van Slyke and Meyer's experiments (1913) 

 which will be briefly summarized. 



They found after injecting intravenously into a dog 1.90 grams of 

 amino acid nitrogen obtained from digested casein, that the blood amino 

 nitrogen rose from 4.05 mg. per 100 c.c. before the injection to 19.7 mg. 

 one-half hour after the injection and came down to 7.85 mg. three and 

 a half hours after the injection. At the same time they also found a 

 rise in the urea nitrogen of the blood, and on examining the tissues of 

 the body they found that their amino acid nitrogen content was increased 

 considerably. Thus in one experiment, after injecting intravenously 

 4.06 grams of amino acid nitrogen they found that the blood amino nitro- 

 gen, thirty minutes after the injection, rose from 3.9 mg. per 100 c.c. 

 to 45.2 mg. In the liver it rose from 31.5 to 93.5, in the muscles from 43 

 to 70 mg., while in the kidneys it rose from 45 to 106 mg. 



From these experiments they concluded that there was a much larger 

 amount of amino nitrogen retained in the tissues than in the blood, and 

 that the tissues abstracted the amino nitrogen from the blood at a rapid 

 rate so as to keep its concentration in the blood at a comparatively low and 

 constant figure. They also concluded that the different tissues have differ- 

 ent powers of absorbing amino nitrogen and that the amino acids are kept 

 in the tissues, either by a process of mechanical absorption or in a loose 

 chemical union with its proteins. 



