364 HAND-BOOK OF PHYSIOLOGY. 



the former as with the latter. In blood, saliva, and other alkaline fluids 

 of the body, phosphates exist in the form of alkaline, neutral, or acid 

 salts. In the urine they are acid salts, viz., the sodium, ammonium, 

 calcium, and magnesium phosphates, the excess of acid being (Liebig) 

 due to the appropriation of the alkali with which the phosphoric acid in 

 the blood is combined, by the several new acids which are formed or dis- 

 charged at the kidneys, namely, the uric, hippuric, and sulphuric acids, 

 all of which are neutralized with soda. 



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 osse- 

 ous tissue the urine derives a large quantity of this salt. The decompo- 

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

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



FIG. 251. Urinary sediment of triple phosphates (large prismatic crystals) and urate of am- 

 monium, from urine which had undergone alkaline fermentation. 



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

 then combined with bases. This 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 on animal or vegetable food, and are 

 diminished after long fasting. The alkaline phosphates are increased 

 after animal food, diminished after vegetable food. Exercise increases 

 the alkaline, but not the earthy phosphates (Bence Jones). Phosphorus 

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

 urine (Ronalds). When the urine undergoes alkaline fermentation, 

 phosphates are deposited in the form of a urinary sediment, consisting 

 chiefly of ammonio-magnesium phosphate (triple phosphate) (Fig. 251). 

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

 is chiefly or wholly derived from the decomposition of urea (p. 359). 



The chlorine of the urine occurs chiefly in combination with sodium, 

 but slightly also with ammonium, and perhaps potassium. As the chlo- 



