60 PROTEIN DIGESTION IN THE INTESTINE 



intestine, the further question arises whether the re- 

 sultant cleavage-products do not undergo either locally in 

 the intestinal wall or in their passage thence into the blood 

 a synthetic reconstruction in such manner that the nitrogen 

 from the intestine comes to be found in the circulatory fluids, 

 not in the form of aminoacids, but in high-molecular com- 

 binations. Attention may be called to the fact that Van 

 Slyke 37 has recently applied his delicate nitric acid method 

 of determination of the aliphatic amino-group (cf . Vol. I of 

 this series, Chemistry of the Tissues, p. 18) to the detec- 

 tion of aminoacid nitrogen in the blood. By this method it 

 has been established that even large amounts of aminoacids 

 injected intravenously disappear very quickly from the 

 blood without anything like an important part appearing in 

 the urine. For example, of twelve grams of alanin injected 

 intravenously there remained after half an hour only a few 

 decigrams in the blood, the rest being apparently transferred 

 into the tissues. Van Slyke concludes from his investiga- 

 tions that the supposition of synthetic change of the amino- 

 acids in the bowel wall is superfluous and that the smallness 

 of the increase of aminoacids in the blood of digesting ani- 

 mals is entirely explicable by the avidity with which these 

 substances are taken up by the tissues and further elaborated 

 by them. 



The results obtained by efforts to arrive at a conclusion 

 in regard to synthetic processes from analytic comparison 

 of the composition of the intestinal mucous membrane of 

 fasting and digesting animals are in no sense consistent. 38 

 It should always be remembered, however, that a number of 

 direct observations indicate the possibility of condensation 

 processes in the intestine. 



87 D. D. Van Slyke, and G. M. Meyer (Rockefeller Instit., New York), 

 Journ. of Biol. Chem., 12, 399, 1912. 



M F. Botaszi, Arch, di Fisiol., 5, 317, 1908; cited in Biochem. CentralbL, 

 8, 374, 1908; E. S. London, Zeitschr. f. physiol. Chem., 61, 69, 1909; P. 

 Glagolew (St. Petersburg), Biochem. Zeitschr., 82, 222, 1910. 



