412 



EXCRETION 



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

 Some are excreted at once; others only after being transformed and incor- 

 porated with the tissues. Calcium and magnesium phosphates form the prin- 

 cipal earthy constituents of bone, and from the decomposition of the osseous 

 tissue the urine derives a quantity of this salt. The decomposition of other 

 tissues also furnishes large supplies of phosphorus to the urine, which phos- 

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

 combined with bases. The quantity is, however, liable to considerable 

 variation. The earthy phosphates are more abundant after meals, w r hether 

 of animal or vegetable food, and are diminished after long fasting. The 

 alkaline phosphates are increased after animal food, diminished after vege- 



FIG. 299. Crystals of Cystin. 



FIG. 300. Crystals of Calcium Oxalate. 



table food. 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 phosphate (triple phosphate), figure 298. 



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

 Next to urea, sodium chloride is the most abundant solid constituent of the 

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

 fluids, their occurrence in the urine is easily understood. 



Occasional Constituents of Urine. Cystin, C 3 H 7 NSO 2 , figure 299, 

 is an occasional constituent of urine. 



Another constituent of the urine is oxalic acid (about 0.02 gram per 

 diem), which is frequently deposited in combination with calcium, figure 

 300, as a urinary sediment. Pathologically, oxalic acid is found to be in- 

 creased in diabetes mellitus, in organic diseases of the liver, and in various 

 other conditions accompanied by derangement of the oxidation mechanism. 



Dextrose and albumin are sometimes present in pathological urine, and are 

 of particular interest from the clinical point of view. See the subject 

 Internal Secretions of the Pancreas, page 459. 



