432 PHYSIOLOGICAL CHEMISTRY. 



or nursing 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 a 

 pale powder. They give the murexid test, and develop much am- 

 monia with caustic soda. 



Calcium-oxalate calculi are, next to uric-acid calculi, the most 

 abundant. They are either smooth and small (HEMP-SEED STONE) 

 or larger, of the size of a hen's egg, with rough, uneven surface, or 

 their surface is covered with prongs (MULBERRY CALCULI). These 

 calculi produce bleeding easily, and therefore they often have a 

 dark-brown surface due to decomposed 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. After strongly heating the powder it 

 is alkaline, due to the production of quick-lime. 



Phosphate Calculi. These, which consist mainly of a mixture 

 of the normal phosphate of the alkaline earths with triple phos- 

 phate, may be very large. They are as a rule of secondary forma- 

 tion, and contain besides these phosphates also some ammonium 

 urate and calcium oxalate. These calculi ordinarily consist of a 

 mixture of these three constituents, earthy phosphate, triple phos- 

 phate, 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. Ca/culi consisting of triple phosphate alone are sel- 

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

 crystalline fracture. Stones of simple-acid calcium phosphate are 

 also seldom obtained. They are white and have a beautiful crystal- 

 line texture. The phosphatic calculi do not burn up, and the pow- 

 der dissolves in acid without effervescence, and the solution gives 

 the reactions for phosphoric acid and alkaline earths. The triple- 

 phosphate calculi generates ammonia on the addition of an alkali. 



Calcium- carbonate calculi occur chiefly in berbivora. They are seldom 

 found in man. They have mostly chalky properties, and are ordinarily white. 

 They are completely or in great part dissolved by acids with effervescence. 



Cystin calculi occur but seldom. They are of primary formation, of vari- 

 ous sizes, sometimes attaining the size of a hen's egg. They have a smooth or 



