214 THE URINE. 



alkali, and as a consequence an increase in the amount of mva 

 occurs directly proportionate to the amount of ammonia formerly 

 present. In herbivorous animals, in which such a vicarious action 

 is never necessary under normal conditions, it is accordingly but 

 little developed, and they hence soon die even after the administra- 

 tion of comparatively small amounts of mineral acids. 



It has been stated that the acid reaction of the urine is essentially 

 due to the presence of acid phosphates. Besides the acid phosphates 

 normal urine, however, contains a certain amount of neutral phos- 

 phates, and it may happen that both are present in equal proportion. 

 But as the neutral phosphates show an alkaline reaction, a neutral 

 point cannot be reached, and such urines hence color red litmus- 

 paper blue, and the blue paper red ; in other words, they are ampho- 

 teric. Such a reaction is not infrequently observed, but is, of course, 

 an accidental occurrence. 



When allowed to stand exposed to the air, every urine undergoes 

 ammoniacal decomposition. This is owing to the action of certain 

 micro-organisms upon urea, which is decomposed, with the forma- 

 tion of ammonia, water, and carbon dioxide, as shown in the 

 equations : 



(1) CO(NH 2 ) 2 + 2H 2 = (NH 4 ) 2 C0 3 . 



(2) (NH 4 ) 2 C0 3 = 2NH 3 + H 2 O + CO 2 . 



The action is thus a hydrolytic decomposition, and is referable to 

 the activity of a special ferment, which is found in the micro-organ- 

 isms in question, notably the Micrococcus urea3 and the Bacterium 

 urese. 



As a result of the presence of free ammonia, the soluble phosphates 

 of the alkaline earths are then precipitated as tricalcium phosphate 

 and as ammonio-magnesium phosphate, and the soluble unites are at 

 the same time transformed into the insoluble ammonium salt. 



At times an increase in the acidity of the urine is observed on 

 standing, and is generally ascribed to a peculiar acid fermentation 

 of contained alcohol, traces of carbohydrates, and the like. More 

 often, however, a decrease in the acidity occurs, even though micro- 

 organisms are absent. This is owing to a decomposition of neutral 

 urates by the acid phosphate of sodium. Acid urates thus result, 

 and may be further decomposed, with the liberation of uric acid. 

 Both urates and uric acid are then thrown down in consequence of 

 the diminished acidity of the fluid, and they are hence no longer 

 capable of influencing the reaction. The changes which here take 

 place may be represented by the equations : 



(1) NaH 2 P0 4 -f- C 5 H 2 Na 2 N 4 O 3 = Na.HPO, + C 5 H 3 NaN 4 O 3 . 



(2) C 5 H 3 NaX 4 3 + NaH 2 PO 4 = Na 2 HPO 4 + C 6 H 4 N 4 O 3 . 



As the reaction of the urine is dependent in the first instance upon 

 the character and the quantity of the food ingested, viz., the amount 



