EXCRETION 321 



and related to the pigments of the bile. The color is 

 deepened in jaundice when the escape of the bile pig- 

 ments by the normal channel is interfered with. It more 

 commonly varies with the degree of dilution. After 

 lively perspiration without water drinking the urine is 

 apt to be high-colored, its dissolved solids being held in 

 a small volume. 



The urine of man when fresh is acid by ordinary 

 standards of measurement. It becomes alkaline on 

 standing because of the bacterial fermentation of urea 

 with formation of ammonium carbonate. When this 

 change is advanced an ammoniacal odor develops and 

 a cloudy deposit may appear. The sediment noticed 

 under these conditions is nothing abnormal. The urine 

 of herbivorous animals is alkaline even when fresh unless 

 the animals are deprived of food. It then becomes acid 

 and the metabolism will naturally have changed to a 

 carnivorous type, the animals living at the expense of 

 their own tissues. 



With an average diet we may expect that about seven- 

 eighths of the nitrogen represented by the compounds of 

 the urine will be in the form of urea. The remainder is 

 divided among several waste-products all more complex 

 than urea and not profitably to be discussed without the 

 assumption of a knowledge of organic chemistry. One of 

 these minor bodies is uric acid, a substance distinguished 

 by its scant solubility and consequent tendency to be 

 retained in the tissues. Some is inevitably formed in 

 the daily metabolism, but the amount can be kept down 

 when desirable by temperance in protein feeding and 

 especially in the consumption of meat. 



All proteins contain sulphur and some contain phos- 

 phorus. Accordingly, when they disintegrate in the 

 body these elements have to be removed. Like the ni- 

 trogen they do not go free but in combinations, the 

 sulphur in several forms but chiefly as sulphates, the 

 phosphorus almost wholly as phosphates. These salts 

 occur in urine together with a considerable amount of 

 21 



