216 URINARY CALCULI. 



The urates are often found mixed with the uric acid 

 deposits or with those of calcium oxalate. The ammonium 

 salt is the most abundant. They are generally small, 

 grayish, and rather soft. They give the murexid test. 

 They are deposited from acid urine, except the am- 

 monium urate, which is formed in an alkaline solution. 



Calcium oxalate concretions are commonly of large 

 size and are very hard. The surface is rough and warty. 

 They are called "mulberry calculi" from the resemblance 

 of the surface to that of the fruit. The urine is generally 

 acid, unless where the presence of the stone has produced 

 cystitis. They are often dark in color from the blood which 

 has been incorporated with them. 



The phosphates can only be present in calculi when 

 the urine is alkaline. They are generally rather soft and 

 easily broken. Calcium phosphate has a chalky appear- 

 ance. Triple phosphate, NH 4 MgP0 4 , is found with other 

 substances. It is more commonly on the outside of the 

 stone, being precipitated by the alkaline reaction produced 

 by the presence of the concretion in the bladder. A mix- 

 ture of the triple phosphate and calcium phosphate is fusi- 

 ble with the blow-pipe and is known as the "fusible cal- 

 culus/' 



Calcium carbonate is not common, although found 

 occasionally. 



The analysis of calculi is made by the use of chemical 

 methods. The stone should be broken or, better, if it is 

 large enough, sawed through the middle. This shows 

 the layers of which it is composed and the nucleus. If 

 there appears to be any difference in the layers, they should 

 be tested separately. Heat a piece upon platinum foil and 

 notice whether it fuses and whether it is combustible or 

 not. If it fuses it is an indication of a phosphate of cal- 



