URINARY CALCULI. 833 



Uric-acid calculi are very abundant. They are variable in size and 

 form. The size of the bladder-stone varies from that of a pea or bean to 

 that of a goose-egg. Uric acid stones are always colored; generally 

 they are grayish-yellow, yellowish-brown, or pale red-brown. The upper 

 surface is sometimes entirely even or smooth, sometimes rough or uneven. 

 Next to the oxalate calculus the uric-acid calculus is the hardest. The 

 fractured surface shows regular concentric, unequally colored layers 

 which may often be removed as shells. These calculi are formed pri- 

 marily. Layers of uric acid sometimes alternate with other layers of 

 primary formation, most frequently with layers of calcium oxalate. 

 The simple uric-acid calculus leaves very little residue when burnt on 

 a platinum foil. It gives the murexid test, but there is no material 

 development of ammonia when acted on by caustic soda. 



Ammonium urate calculi occur as primary calculi in new-born or nurs- 

 ing infants, rarely in grown persons. They often occur as a secondary 

 formation. The primary stones are small, with a pale yellow or dark- 

 yellowish surface. When moist they are almost like dough; in the 

 dry state they are earthy, easily crumbling into pale powder. They 

 give the murexid test and develop much ammonia with caustic soda. 



Calcium-oxalale calculi are, next to uric-acid calculi, the most abundant. 

 They are either smooth and small (HEMP-SEED CALCULI) or larger, of the 

 size of a hen's egg, with rough, uneven surface, or their surface is cov- 

 ered with prongs (MULBERRY CALCULI). These calculi produce bleeding 

 easily, and therefore they often have a dark-brown surface due to decom- 

 posed blood-coloring matters. Among the calculi occurring in man 

 these are the hardest. They dissolve in hydrochloric acid without 

 developing gas, but are not soluble in acetic acid. After gently heating 

 the powder, it dissolves in acetic acid with frothing. With more intense 

 heat it becomes alkaline, due to the production of quicklime. 



Phosphate Calculi. These, which consist mainly of a mixture of the 

 normal phosphate of the alkaline earths with triple phosphate, may be 

 very large. They are as a rule of secondary formation and contain 

 besides these phosphates also some ammonium urate and calcium oxalate. 

 These calculi ordinarily consist of a mixture of three constituents 

 earthy phosphate, triple phosphate, and ammonium urate surrounding 

 a foreign body as a nucleus. Their color is variable white, dingy white, 

 pale yellow, sometimes violet or lilac-colored (from indigo red). The 

 surface is always rough. Calculi consisting of triple phosphate alone 

 are seldom found. They are ordinarily small, with granular or radiated 

 crystalline fracture. Stones of mono-acid calcium phosphate are also 

 seldom obtained. They are white and have beautiful crystalline texture. 

 The phosphatic calculi do not burn up, the powder dissolves in acid 

 without effervescence, and the solution gives the reactions for phos- 



