PROTEIN METABOLISM 761 



Jacobson, which connects the lower branches of the portal vein with, as a 

 rule, the left renal vein (Fig. 354). On this account the liver can be cut 

 out of the body or of the circulation without entailing the rapid death of the 

 bird, which may live for three or four days, and pass urine after the opera- 

 tion. The urine is, however, fluid, and the uric acid, instead of accounting 

 for 60 per cent, of the total nitrogen, now forms only 5 per cent. The place 

 of the greater part of the uric acid has been taken by ammonium lactate, 

 which therefore seems to be the chief immediate precursor of the uric acid in 



Iliac vein- 

 Kidney- 



I- Inf. Vena Cava 



Portal v. 



V of Jacobson 

 Inf. mes.v. 



Caudal v. 



Rectum 



FIG. 354. Diagram to show the arrangement of the veins in the bird, 

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

 MORAT.) 



the urine of birds. We shall have occasion to consider the method of trans- 

 formation of ammonium lactate to uric acid more fully when dealing with 

 the origin of the latter body. 



Of late years evidence has been brought forward that the formation of 

 ammonia from the amino-acids may involve no such profound changes of 

 oxidative disintegration as were suggested in the theories of Hofmeister or 

 Schroder. If amino-acids be treated with the pulp of various organs the 

 amount of ammonia in the mixture is increased, 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 rapid con- 

 version of the nitrogen of the ingested protein into urea. Viewed in this light, 



* According to van Slyke, the liver plays the chief part in the breakdown of the 

 amino-acids, though there is no reason to deny the possession of similar power to the 

 other tissues (e.g. muscles) of the animal body. 



