CHAPTER IV. 



DEAMINIZATION. 

 General. 



THE question of deaminization of the protein molecule must now be 

 dealt with. Evidence has been gradually accumulating which points 

 to the deaminizing capacity of the tissues, as being one of the funda- 

 mentally important activities. It has long been known that shortly 

 after the ingestion of protein there follows a marked rise in the output 

 of nitrogen in the urine for the most part in the form of urea (see 

 p. 77). The cause of this rise has long been a matter of speculation : 

 did this nitrogen come from the protein ingested, or did it come from 

 the tissues? The work of Nencki and his school helped to show with 

 some degree of certainty the important part played by the ingested 

 protein digestion products, but it was not until modern experimental 

 methods were introduced, such as those of Lang, that more or less 

 direct evidence was obtained in favour of the view that the urea could 

 come direct from the ammonia liberated by the deaminizing activities 

 of certain of the tissues. To meet the objection that the energy loss 

 would be considerable if an extensive deaminization took place, direct 

 estimations of the energy value of certain amino acids and of the pro- 

 ducts resulting from deaminization have been carried out. The follow- 

 ing table drawn up by Leathes l shows that no material loss occurs : 



1 Leathes, " Problems in Animal Metabolism," p. 154. 

 49 



