228 THE URINE. 



of the blood, in the carnivorous animals at least, remains constant, 

 but the elimination of urea is proportionately less, and the deficit of 

 nitrogen in this form appears as ammonia in combination with acids 

 (lactic acid). 



By gradually increasing the amount of acid it is thus possible to 

 bring about the almost complete disappearance of urea from the 

 urine. A point, however, is finally reached where the animal suc- 

 cumbs to acid intoxication. Death in such cases results from tissue- 

 suffocation, as there is not sufficient alkali left in the lymph and 

 plasma to combine with the carbon dioxide in the tissues. 



Conversely, it is possible to cause the ammonia to disappear from 

 the urine by the administration of a sufficiently large quantity of 

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

 which is 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. 



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 . 



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 urates 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 + C 6 H 2 Na 2 N 4 O s = Na,HPO 4 + C 5 H 3 NaN 4 O 8 . 



(2) C 5 H 3 NaN 4 O 3 -f 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 



