346 



PHYSIOLOGICAL CHEMISTRY. 



p. 348) are often mistaken for crystals of calcium phosphate. We 

 may differentiate between these two crystalline forms by the fact 

 that acetic acid will readily dissolve the phosphate, whereas the urate 

 is much less soluble and when finally brought into solution and re- 

 crystallized one is frequently enabled to identify uric acid crystals 



FIG. 100. 



CALCIUM CARBONATE. 



which have been formed from the acid urate solution. The clinical 

 significance of the occurrence of calcium phosphate crystals in the 

 urinary sediment is similar to that of "triple phosphate" (see 

 page 344). 



Calcium Sulphate. Crystals of calcium sulphate are of quite 

 rare occurrence in the sediment of urine. Their presence seems to 

 be limited in general to urines which are of a decided acid reaction. 

 Ordinarily it crystallizes in the form of long, thin, colorless needles 

 or prisms (Fig. 95, page 298) which may be mistaken for calcium 

 phosphate crystals. There need be no confusion in this respect, 

 however, since the sulphate crystals are insoluble in acetic acid 

 which reagent readily dissolves the phosphate. As far as is known 

 their occurrence as a constituent of urinary sediment is of very 

 little clinical significance. 



Uric Acid. Uric acid forms a very common constituent of the 

 sediment of urines which are acid in reaction. It occurs in more 

 varied forms than any of the other crystalline sediments (Plate V, 

 opposite page 273, and Fig. 101, page 347), some of the more com- 

 mon varieties of crystals being rhombic prisms, wedges, dumb-bells, 



