CHAP, in.] ELIMINATION OF WASTE PRODUCTS. 521 



By an average Per 1 kilo 



man of 66 kilos. of body weight. 



Total Solids (continued) 



Sulphuric Acid 2-012 -0305 



Phosphoric Acid 3-164 -0480 



Chlorine 7-000 -1260 



(8-21) 



Ammonia *770 



Potassium 2-500 



Sodium 11-090 



Calcium -260 



Magnesium *207 



72-000 



327. The Acidity of Urine. The healthy urine of man is 

 acid, owing to the presence of acid sodium phosphate, the ab- 

 sence of free acid being shewn by the fact that sodium hyposul- 

 phite gives no precipitate. The amount of acidity is about 

 equivalent to 2 grms. of oxalic acid in twenty-four hours, but 

 the degree of acidity at any one time varies much during the 

 day, being in an inverse ratio to the amount of acid secreted by 

 the stomach ; thus it decreases after food is taken, and increases 

 again as gastric digestion comes to an end. It varies with the 

 nature of the food ; with a vegetable diet the excess of alkalis 

 in the food, being secreted by the urine, leads to alkalinity, or 

 at least to diminished acidity, whereas this effect is wanting 

 with an animal diet, in which the alkalis are less abundant, 

 earthy bases preponderating. Hence the urine of carnivora is 

 generally very acid, while that of herbivora is alkaline. The 

 latter, when fasting, are for the time being carnivorous, living 

 entirely on their own bodies, and hence their urine becomes 

 under these circumstances acid. 



The natural acidity increases for some time after the urine 

 has been discharged, owing to the formation of fresh acid, appar- 

 ently by some kind of fermentation. This increase of acid fre- 

 quently causes a precipitation of urates, which the previous 

 acidity, even after the cooling of the urine, had been insufficient 

 to throw down. After a while however the acid reaction 

 gives way to alkalinity. This is caused by a conversion of the 

 urea into ammonium carbonate through the agency of a specific 

 'organized' ferment. This ferment as a general rule does 

 not make its appearance except in urine exposed to the air ; it 

 is only in unhealthy conditions that the fermentation takes 

 place within the bladder, and in such cases is due either to 

 micro-organisms introduced into the bladder from without, 

 during the use of instruments for instance, or to the action of 

 an unorganized ferment, secreted apparently by the walls of the 

 bladder. 



