ALBUMINS OR PROTEINS. 241 



theless, be relegated to the background. Even if such a process does 

 take place, the amount produced thereby is so small in comparison with 

 that obtained from other sources, that it possesses little significance. 

 Wiener has also tried to show that uric acid is synthetically produced by 

 znammals. His conclusions have, however, been contradicted. 1 The 

 synthetic production of uric acid by the mammalian organism cannot, at 

 present, be accepted with certainty. 



The question now arises, In what organs does the uric acid formation 

 take place? The liver seems to play an important part in this process 

 among birds. W. v. Schroder 2 extirpated the kidneys from hens, and 

 succeeded in keeping these birds alive for 5-10 hours. Schroder examined 

 after their death the blood and organs for uric acid, and found that a very 

 appreciable accumulation of this acid had resulted. The uric acid pro- 

 duction had evidently continued after the extirpation of the kidneys. 

 The same behavior was noticed with snakes. It seems, therefore, that 

 the kidneys are of little, or even no, service in this process. This de- 

 cision was the more striking, as the kidneys were for a long time looked 

 upon as the most important place for the production of uric acid. This 

 opinion had originated from the way uric acid is distributed after the 

 ureter has been ligated. 



Both of the albumin metabolic substances so far considered are con- 

 nected with the whole albumin molecule and all its cleavage-products. 

 Ammonia ought also to be included in this group, as it occurs in varying 

 quantities in urine. It was formerly believed that an increased elim- 

 ination of ammonia indicated an insufficient production of urea. Little 

 by little the cause was more accurately investigated, and it was dis- 

 covered that the increase in the amount of ammonia was not a primary 

 effect, but that it was due to an increased production of acid. Thus, in 

 a diabetic, the appearance of acetoacetic acid and of /?-hydroxy-butyric 

 acid is associated with an increased elimination of ammonia. F. Walter 3 

 even showed that the administration of hydrochloric acid to human 

 beings and dogs caused an increased elimination of ammonia. A. 

 Schittenhelm and. A. Katzenstein 4 have recently shown that the amount 

 of ammonia present in the urine is directly related to the total nitrogen of 

 the urine. It rises and falls with the consumption of albumin, so that the 

 ratio of ammonia to the total nitrogen remains constant within narrow 

 limits. The amount of ammonia excreted is not affected by the admin- 

 istration of urea or ammonium carbonate. It is also interesting to note 

 that, not only does an increased elimination of ammonia follow an increased 



1 Cf. R. Burian: Z. physiol. Chem. 43, 497 (1905). 



2 Arch. Anat. Physiol. 1880, p. 113, Supplement. 



3 Loc. cit. 



4 Arch. exp. Path. Therapie, 2, 541 (1905). 



