On the Differences in the Structure of Calculi. 169 



at rest, and therefore ^ealculi from the kidneys are never 

 composed of the phosphates. 



In a few instances, calculi from the kidneys, composed of 

 oxalate of lime, are voided ; but this is a very rare occur- 

 rence : of three preserved in the Hunteiian collection, two 

 are extremely small and hard, having an appearance of being 

 made up of several smaller calculi, of a dark brown colour. 

 The third is of the size of a small pea, its surface smooth, 

 and of a gray colour, and not very hard. 



Section II. 

 Of Calculi which have leen retained in the Kidney. 

 When one or more of the. calculi described in the pre- 

 ceding section are detained in the infundibula or pelvis of the 

 kidney, it frequently happens that they increase in that si- 

 tuation to a considerable size. 

 This increase is of two kinds. 



1. Where there is a great disposition to the formation of 

 uric acid, the calculus consists wholly of that substance and 

 animal matter, so as frequently to form a complete cast of 

 the pelvis of the kidney. 



2. Where there is less disposition to form uric acid, the 

 external laminae are composed of the ammoniaco-magnesian. 

 phosphate, and phosphate of lime. 



In one instance, a small uric calculus had been deposited 

 in the kidney, in such a situation that its upper surface was 

 exposed to a continual stream of urine, upon which beau- 

 tiful crystals of the triple phosphate had been deposited. It 

 would therefore seem, that, under common circumstances, 

 a stream of urine passing over a calculus of uric acid has a 

 tendency to deposit the phosphate upon it. 



Section III. 

 Of Calculi of the urinary Bladder. 

 Calculi met with in the bladder are of four kinds. 



1. Those formed upon nuclei of uric acid, from the kidnev. 



2. Thqse formed upon nuclei of oxalate of lime, from the 

 kidney. 



3. Those formed upon sand or animal mucus, deposited 

 in the bladder, 



4. Those 



