172 RESPIRATION 



animals also ultimately became comatose, just as is the case when 

 CO 2 is in great excess ; and finally there were signs of exhaustion 

 of breathing, the breathing ceasing before the heart ceased to beat. 



Another very important result reached in these investigations 

 was that when the experiments were repeated on dogs it was much 

 more difficult to produce the symptoms, and it was found that the 

 amount of ammonia excreted (in combination with acid) in the 

 urine was increased greatly. Under normal conditions the amount 

 of nitrogen excreted as ammonia is small in proportion to the total 

 excretion of nitrogen. Thus in man the amount of ammonia 

 usually excreted in 24 hours is only about 0.7 gram (sufficient, 

 however, to neutralize about 2 grams of H 2 SO 4 ), so that only a 

 small fraction of the total nitrogen is excreted as ammonia. In 

 acid poisoning, however, the fraction becomes a very much 

 larger one in carnivorous animals and in man. Walter found that 

 in dogs the ammonia excretion could be pushed up to several 

 times the normal by giving large doses of acid. 



According to the existing evidence, which originated with 

 Schmiedeberg and his pupils, ammonia is converted into urea in 

 the liver. It appears, therefore, that when acid is administered to 

 carnivorous animals or men, ammonia is not converted into urea, 

 or else nitrogen which normally appears as urea is converted into 

 ammonia and goes to neutralize the acid. If ammonia is admin- 

 istered by mouth as carbonate it is wholly converted into urea, and 

 the excretion of ammonia by the urine may be actually diminished. 

 If, on the other hand, the ammonia is administered in combination 

 with a strong acid as a neutral salt, much of this ammonia appears 

 as salts of ammonia in the urine. Some is, however, converted into 

 urea in the liver, as was recently shown definitely by perfusion 

 experiments. 2 It was found that during health the proportion 

 of ammonia which escapes conversion into urea and consequently 

 appears in the urine depends on the acid-forming or alkali- 

 forming properties of the diet. Thus with a meat diet the pro- 

 portion of ammonia is much higher than with a vegetable diet; 

 and by administering alkalies ammonia may be made to disappear 

 entirely from the urine. 



The varying neutralization of acids by ammonia is therefore 

 one of the means by which the reaction within the body is regu- 

 lated in man and carnivorous animals, while variation in the 

 excretion of acid or alkali in the urine is another. The former 

 means hardly exists in herbivorous animals. But the significance 



'Loffler, Biochem. Zetischr., LXXXV, p. 230, 1918. 



