alsberg: biochemical analysis of nutrition 



found that there is an equilibrium between these — sub- 

 stances, so that where one is -ent in solution ther- - 

 found a definite amount of the other. I easy stej :: >m 



ammonium carbamate to urea. Thus the amino group split off 

 from the ami no-acid in the intestinal wall or elsewher- ri- 



mately converted into urea and excreted. There are probably 

 other methods of the formation of lire:: 3 xample 



cleavage from arginine which con* guanidir. _ ingclos 



related to urea. After the removal of the amino group from the 

 amino-acids there is lei" arbona - -idue which may be 

 burned to furnish energy, perhaps directly, perhap- n- 



version into sugar. A portion of the amino-aeic - - rbed 

 the intestines is not. however, deprived of its nitrogen, but passes 

 into the blood stream from which it :»rbed by each indi- 



vidual cell according to that cell's particular needs. The cell 

 then reconstructs from these amino-ac: h its wn ch ric 



protein. Thus it is possible to explain in a comparatively sim- 

 ple manner how. for example, wheat protein when fed t 

 animal is converted into the characteristic proteins of that ani- 

 mal. It is done by the cells of the tissues from amino-: : Is 

 supplied to the cells by the blood,, the blood receiving the amir - 

 acids from the intestinal wall. 



This theory concerning the fate of food proteins in the ani- 

 mal body is supported by certain very interest!: a a x"peri- 

 ments. In these experiments animals, usually whit- - were 

 fed upon definite mixtures containing only a few pure food 

 substances. These mixtures consisted of sugai I mineral 

 salts, and a single pure protein. In each set oi experiments a 

 different pure protein was used in each series, all oi 

 remaining constant. It is in this way possible to determine 

 the nutritive value of individual proteins. The results of 1 - 

 work indicate that many proteins are incapable either 

 of supporting life or of producing growth. On the whole 

 it may be said that many more vegetables than animal 

 proteins are defective in this wa Now, when the compo-:- 

 tion of such defective proteins is compared with that of 

 proteins that are not defective in this respect, it is found thj I 



