860 PHYSIOLOGY 



an increase which is absent when no amino-acids are added. More 

 ammonia, for instance, was found when leucine, glycine, tyrosine, or 

 cystine was added to the pulp. On the other hand, phenylalanine 

 gave rise to no production of ammonia. This conversion was ascribed 

 by Lang to the presence of a deaminising ferment in the cells of 

 these different tissues, and Leathes and Folin have suggested that 

 this process of deamination is the essential factor in the production of 

 the excess of ammonia in the portal blood and in the rapid conversion 

 of the nitrogen of the ingested protein into urea. Viewed in this 



I- Inf. Vena Cava 



Iliac 



vein- 



Kidney 



V. of Jacobson 

 Inf. mes.v. __ 



Caudal \ 



Rectum 



FIG. 352. Diagram to show the arrangement of the veins in the bird, 

 with the communication of the renal and portal veins. (After 

 MORAT.) 



light, these results of Lang, Nencki, and others effect an entire 

 revolution in our views of protein metabolism. Instead of regard- 

 ing the urea which appears in the urine after protein ingestion 

 as produced by the total disintegration of the protein molecule, 

 we see now that it represents merely the throwing off of the nitro- 

 genous part of this molecule. This deamination may be a purely 

 hydrolytic change or it may be associated with oxidation or reduction. 

 Deaminisation of alanine, for instance, by simple hydrolysis would 

 result in the formation of lactic acid (an oxy-fatty acid). 



CH 3 



CH, 



CH.NH 2 + H 2 = NH 3 + CHOH 



COOH 



COOH 



