58 PROTEIN DIGESTION IN THE INTESTINE 



and therefore that it is not in any sense a "purposeless waste 

 of energy. ' ' 



Residual Nitrogen. It might very properly be supposed 

 that, in case the aminoacids resulting from the advanced pro- 

 tein dissociation are actually resorbed as such, it would be a 

 matter of little difficulty in an animal in the midst of diges- 

 tive activity to detect a notable increase of residual nitrogen 

 in the blood in the form of incoagulable compounds. 28 As a 

 matter of fact, however, this is very difficult. G. v. Bergman 

 and Langstein 29 have calculated that, if, as supposed, tissue 

 assimilation proceeds in full harmony with resorption, only a 

 few hundredths of one per cent, of aminoacids in the portal 

 blood will suffice to cover the total nitrogen transportation 

 from intestine to the blood required for protein metabolism. 

 0. Cohnheim believes that it may be concluded from observa- 

 tions upon the rapidity of meat digestion and the rapidity of 

 blood circulation that even with the most active absorption 

 and if no other tissues were involved not more than 0.03 g. 

 of albumin or protein dissociation products could be taken 

 up in a litre of blood. 30 According to an investigation con- 

 ducted under the direction of Hofmeister 31 the residual 

 nitrogen of the blood may be reduced to three fractions: 

 urea, "albumoses" precipitable by tannin, and aminoacids 

 (not precipitated by tannin) . The bulk, actually about three- 

 fourths, of the residual nitrogen in the blood of either the 

 fasting or of the digesting dog, consists of urea. Of the 

 other two fractional parts that of the aminoacids always 

 shows definite increase during digestion. The albumose 

 fraction is an inconstant one ; even after feeding albumoses 

 no increase was noted indicative of their entrance to the 



38 Literature upon the Incoagulable Nitrogen-containing Bodies of the 

 Blood Serum: P. Morawitz, Handb. d. Biochem., 2", 80-86, 1909. 



1. c. 



30 O. Cohnheim, Physiol. d. Verd. u. Ernahr., p. 227, 1908. 



31 H. Hohlweg and H. Meyer (Physiol. Chem. Instit., Strassburg), Hof- 

 meister's Beitr., 11, 381, 1908. 



