206 Brande on the Medico-Chemical 



that it remains for any time without undergoing an increase of 

 bulk, the nature of which will chiefly depend upon the state of 

 the urine, which, if charged with uric acid, will deposit it in 

 layers', thus causing the growth of the calculus in that sub- 

 stance ; or if there be no excess of uric acid, the deposition 

 will be of the phosphates. Accordingly, bladder calculi are 

 sometimes almost entirely composed of uric acid, while at others 

 the nucleus only is of uric acid, and the bulk of the stone con- 

 sists of the triple phosphate of ammonia and magnesia, and 

 phosphate of lime, forming the mixture which Dr. Wollaston, 

 in his valuable paper, has terraedi fusible calculus ; (Phil. Trans. 

 1797,) and in which the ammtfnio-magnesian salt generally 

 predominates. 



It deserves notice, as throwing considerable light upon the 

 formation and growth of cystic calculi, that the urine has at all 

 times a tendency to deposit the above-mentioned phosphate 

 upon any body over which it passes : drains by which urine 

 is carried off from the streets, Sfc, are often incrusted with its 

 regular crystals ; and in cases where extraneous bodies have 

 got into the bladder, they have often in a very short time be- 

 come considerably enlarged by the deposition of the same sub- 

 stance. If, from any cause, the urine becomes in the slightest 

 degree putrid, ammonia is evolved, and the deposition of the 

 phosphates much accelerated and increased. These, as we shall 

 afterwards show, are facts that require always to be borne in 

 mind, as influencing the mode of treatment to be adopted in 

 respect to bladder calculi in general. 



The appearance of the triple phosphate is more or less crys- 

 talline, and the calculi incrusted with it are generally grayish 

 white. Strongly heated before the blow-pipe, this substance 

 evolves ammonia, and with much difficulty enters into an im- 

 perfect fusion ; if, however, phosphate of lime be present, it 

 more readily undergoes fusion : hence the propriety of the 

 teim fusible calculus applied to tlie mixture of the two phos- 

 phates. 



Calculi, composed entirely of the aramonio-magnesian phos- 

 phate, are very rare ; I have seen two ; they were crystallized 



