PROTEIN AND CIRCULATION 73 



ARE AMINO ACIDS FOUND IN THE BLOOD? 



Opposed to the investigators advancing the regenera- 

 tion of protein immediately after absorption is a 

 second group of men who have long believed that 

 amino acids are absorbed into the blood. The great 

 difficulty has been to demonstrate their presence. A 

 large number of experiments have been devised in 

 various ingenious ways to overcome the difficulties 

 attendant upon such a procedure. Many investigators 

 have obtained partial evidence of the presence in the 

 blood stream but an actual isolation and identification 

 of individual amino acids was for a long time lacking. 



The failure to obtain definite proof of the amino 

 acids in the blood has been due in large measure to 

 the inadequacy of the methods available. At any one 

 moment the quantity of these substances in a deter- 

 mined sample of blood must be exceedingly small. 



Moreover, one must remember that the formation of 

 amino acids in the intestinal tract is a gradual process 

 and not of the nature of an explosion so that the 

 quantity of amino acids available for passage into the 

 blood during a given period must be relatively small. 

 The rapidity of circulation is another factor to be 

 taken into consideration. It has been shown that in 

 the portal vein of the dog the blood travels at the rate 

 of about 150 cc. per minute. Pfluger has estimated 

 that for human beings a maximum rate of absorption 

 of protein may be represented at 1.14 gram protein 

 per kilo per hour. If the 1.14 gram protein absorbed 



