PROTEIN METABOLISM 859 



canal had first to pass through the general circulation. A certain 

 number of animals were found to be particularly susceptible to the 

 nature of their diet. On a diet largely consisting of carbohydrates 

 they maintained good health. After a large meat meal, however, they 

 became ill, and in many cases suffered from tremors and convulsions 

 ending in coma. At the same time there was a definite increase of 

 ammonia in the urine, chiefly in the form of ammonium carbamate. 

 Analysis of the blood from a normal animal shows that during protein 

 digestion there is a constant excess of ammonia in the blood of the 

 portal vein above that in any other part of the vascular system. In 

 the carotid blood the normal amount, according to Nencki, is about 

 2 mg. per 100 c.c., in the portal blood 4 to 6 mg. During the 

 morbid symptoms brought on by a protein meal in the animals in 

 whom an Eck fistula has been produced, the ammonia in the carotid 

 blood may rise to as much as 4 mg., i.e. to the amount normally 

 found in portal blood. Pawlow and Nencki therefore ascribed the 

 symptoms observed in these dogs after a heavy meat meal to a condi- 

 tion of ' ammoniaemia,' and regarded the liver as an organ which is 

 normally concerned in protecting the rest of the body from ammonia 

 produced in the alimentary tract by converting this substance into 

 the innocuous neutral body, urea. 



This view of the function of the liver is confirmed by Schroder's 

 experiments on birds. In these animals the chief nitrogenous excretion 

 is not urea, but ammonium urate, 60 per cent, of the nitrogen of the 

 urine appearing in the form of uric acid. In birds there is naturally 

 a communication between the portal system and the general venous 

 system by means of the vein of Jacobson, which connects the lower 

 branches of the portal vein with, as a rule, the left renal vein (Fig- 352). 

 On this account the liver can be cut out of the body or of the circu- 

 lation without entailing the rapid death of the bird, which may live 

 for three or four days, and pass urine after the operation. The urine 

 s, 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 the urine of birds. We 

 shall have occasion to consider the method of transformation 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 forma- 

 tion 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, 



