URINARY CALCULI. 557 



an alderman of Dublin, and which almost completely filled the 

 bladder, that weighed several pounds.* The surface is sometimes 

 smooth and polished and sometimes rough, being covered with 

 numerous tubercles. The colour is sometimes brown, sometimes 

 white, and in the mulberry calculi almost black. Sometimes they 

 are studded with crystals of ammonia-phosphate of magnesia. 

 The specific gravity, according to Fourcroy, varies from 1'213 

 to 1-976.| 



In general, when a calculus is sawn in two, we perceive that 

 it is composed of a number of concentric layers, covering a nu- 

 cleus. These layers (together with the nucleus) are sometimes 

 all composed of the same matter ; but more frequently the nu- 

 cleus consists of a substance quite different from the concentric 

 layers that cover it. Uric acid and oxalurate of lime are very 

 common nuclei. The concentric layers are sometimes composed 

 of the same materials ; but frequently also of different materials. 

 Thus they may consist of uric acid or phosphate of lime, or triple 

 phosphate, or of two or more of these intermixed. 



The urinary calculi hitherto observed may be conveniently 

 arranged under the following genera : 



1. Uric acid calculi. Their most common colour is brown, 

 differing somewhat in the depth of shade. But this is not always 

 the case, for I have in my possession several small uric acid cal- 

 culi passed per urethram, almost as white as chalk. The surface 

 is sometimes smooth and polished, but not unfrequently tubercu- 

 lar. The specific gravity varies from 1*5 to 1786. But some- 

 times it is as low as 1-276. It is usually composed of concentric 

 laminae, differing in thickness and exactly resembling each other. 

 Each lamina is composed of fibres, (or small crystals,) so placed 

 as to be perpendicular to the central point of the calculus. 

 Judging from the collections of calculi which I have seen, 

 (amounting in all to not fewer than 1000,) this is by far the most 

 common of all the urinary calculi. 



Uric acid calculi are very sparingly soluble in water ; requir- 

 ing at least ten thousand times their weight of that liquid. But 

 they dissolve readily in caustic potash or soda ley, especially 



Sir James Earl describes a stone taken out of the bladder after death that 

 must have been larger than this. It filled the bladder, and weighed 3 Ibs. 4 oz. 

 troy. It consisted of a congeries of calculi united together. It was composed 

 chiefly of triple phosphate. See Phil. Trans. 1809, p. 303. 



f Systeme, x. 213. 



