The recent trend of investigation in the field of metabolism has served to demonstrate the importance of the amino acids in the metabolism of the proteins. As was shown by Folin and Denis1 and Van Slyke and Meyer,2 amino acids are present normally in the blood. Final proof of this fact was furnished by Abderhalden,3 who succeeded in isolating and identifying several of this group of compounds from large amounts of blood, and by Abel, Rowntree and Turner,4 who obtained considerable quantities of amino acids from blood by their ingenious method of vividiffusion. From these and other observations the conclusion has been drawn that the digested proteins of the food are absorbed as amino acids and as such are transported to the tissues.
The amounts of amino acid nitrogen in the blood of different normal individuals or even of the same individual at different times have