55S MORBID CONCRETIONS. 



when assisted by heat, and the uric acid is precipitated from the 

 solution by all acids, even by the acetic. 



2. Urate of ammonia calculi. These calculi, so far as I have 

 seen them, are all small. They are whitish or clay-coloured, 

 and composed of concentric coats. They have usually a uric 

 acid neucleus, and probably contain uric acid mixed with the 

 urate of ammonia. According to Fourcroy and Vauquelin, their 

 specific gravity varies from 1-228 to 1-720. They are obviously 

 rare ; as there is not a single specimen in the Hunterian collec- 

 tion, consisting of several hundred calculi. It was this circum- 

 stance, probably, that led Mr Brande to conclude that no calculi 

 composed of urate of ammonia exist. 



Laugier, in 1824, analyzed a calculus taken out of the blad- 

 der after death. It was brown, soft, and friable, and could only 

 be extracted in fragments. Laugier found its constituents to be, 

 Uric acid, . . 10 



Urate of ammonia, . . 40 

 Phosphate of ammonia, . 5 



Oxalate of lime, . .15 

 Animal matter, . . 20 

 Moisture and loss, . .10 



100* 



Boutron-Charlard also found urate of ammonia in a urinary 

 calculus, f 



3. Phosphate of lime calculi. This calculus, first determined 

 and described by Dr Wollaston, is much less frequent than uric 

 acid calculi. The colour is usually a pale brown, and the sur- 

 face is quite smooth and polished. It is composed of concentric 

 laminae, in general adhering so slightly to each other as to se- 

 parate with ease into concentric crusts. The surface of each of 

 which, like that of the outermost, is quite smooth. The lamina? are 

 sometimes striated in a direction perpendicular to the surface. 



When this calculus is ignited it becomes black, in consequence 

 of the charring of the animal matter which it contains, but it 

 soon burns white, and remains unaltered before the blowpipe, 

 unless a very high temperature be applied, when it may be fused. 

 It is more easily fusible than the earth of bones, because it con- 

 tains little or no carbonate of lime. When in powder it dissolves 

 readily in nitric or muriatic acid. 



* Jour, de Pharmacie, x. 258. f Ibid. xxii. 556. 



