152 PRACTICAL PHYSIOLOGY. [XXIV. 



7. B. Incombustible. 



(i.) Urates (Na, Ca, Mg), are rarely met with as the sole con- 

 stituent. They give the nmrexide test. 



(ii.) Oxalate of Lime or mulberry calculi, so called because 

 their surface is usually tuberculated or warty ; they are hard, 

 dark-brown, or black. These calculi, from their shape, cause 

 great irritation of the urinary mucous membrane. When in the 

 form of gravel, the concretions are usually smooth, variable in 

 size, pale-grey in colour. Layers of oxalate of lime frequently 

 alternate with uric acid. When heated it blackens, but does not 

 fuse, and then becomes white, being converted into the carbonate 

 and oxide. The white mass is alkaline to test-paper, and when 

 treated with HC1, it effervesces (C0 2 ). Oxalate of lime is not 

 dissolved by acetic acid. 



(iii.) Carbonate of Lime. Rare in man; when met with, they 

 usually occur in large numbers. Dissolve with effervescence in 

 HC1. Sometimes crystals occur as a deposit. They are common 

 in the horse's urine. 



(iv.) Basic Phosphate of Lime Calculi are very rare, and are 

 white and chalky. 



(v.) Mixed Phosphates (Fusible Calculus) consist of triple- 

 phosphate and basic phosphate of lime. They indicate that the 

 urine has been ammoniacal for some time, owing to decomposi- 

 tion of the urea. They are usually of considerable size, and 

 whitish; the consistence varies. When triple-phosphate is most 

 abundant, they are soft and porous, but when the phosphate of 

 lime is in excess, they are harder. A whitish deposit of phos- 

 phates is frequently found coating other calculi. This occurs 

 when the urine becomes ammoniacal, hence in such cases regard 

 must always be had to the condition of the urinary mucous 

 membrane. Such calculi are incombustible, but, when exposed to 

 a strong heat, fuse into a white enamel-like mass, hence the name, 

 fusible calculi. 



8. (B.) Group. 



(i.) The substance gives the murexide reaction, indicates urates. 



The residue is treated with water. 



It is soluble, and ( Neutralise ; add platinic chloride, a yel- \ -& . 

 the solution is] low precipitate . . . . ./" 

 alkaline . . ( The residue yields a yellow flame . = Sodium. 



f Ammonium oxalate gives a white crys- I n -, . 



Scarcely soluble;! talline precipitate . . . .I""- m * 

 the solution is | Ammonium oxalate gives no precipitate, 

 scarcely alka- -J but on adding ammonium chloride, 

 line ; soluble in sodic phosphate, and ammonia, there ^ = Magnesium. 

 acetic acid . j is a crystalline precipitate of triple- 

 phosphate .... 



