EXCRETION". 



481 



The phosphates are taken largely in both vegetable and animal food; 

 some thus taken are excreted at once; others, after being transformed 

 and incorporated with the tissues. Calcium phosphate forms the prin- 

 cipal earthy constituent of bone, and from the decomposition of the 

 osseous tissue the urine derives a large quantity of this salt. The de- 

 composition of other tissues also, but especially of the brain and nerve- 

 substance, furnishes large supplies of phosphorus to the urine, which 

 phosphorus is supposed, like the sulphur, to be united with oxygen, and 

 then combined with bases. The quantity is, however, liable to consid- 

 erable variation. Any undue exercise of the brain and all circumstances 

 producing nervous exhaustion increase it. The earthy phosphates are 

 more abundant after meals, whether of animal or vegetable food, and 

 are diminished after long fasting. The alkaline phosphates are in- 



Fig. 305. Crystals of Cystin. 



Fig. 306. Crystals of Calcium Oxalate. 



creased after animal food, diminished after vegetable food. Exercise 

 increases the alkaline, but not the earthy phosphates. Phosphorus 

 uncombined with oxygen appears, like sulphur, to be excreted in the 

 urine. When the urine undergoes alkaline fermentation phosphates are 

 deposited in the form of a urinary sediment, consisting chiefly of 

 ammonio-magnesium phosphates (triple phosphate) (fig. 304). The 

 compound does not, as such, exist in healthy urine. The ammonia is 

 chiefly or wholly derived from the decomposition of urea. 



(c.) The Chlorine of the urine occurs chiefly in combination with 

 sodium (next to urea, sodium chloride is the most abundant solid con- 

 stituent of the urine), but slightly also with ammonium, and, perhaps, 

 potassium. As the chlorides exist largely in food, and in most of the 

 animal fluids, their occurrence in the urine is easily understood. 



Occasional Constituents.^^ (CsEWST S0 2 ) (fig. 305) is an 

 occasional constituent of urine. It resembles taurin in containing a 

 large quantity of sulphur more than 25 per cent. It does not exist in 

 healthy urine. 



Another common morbid constituent of the urine is Oxalic acid, 

 3 1 



