22 S Mr. W. Brande on the Differences 
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 been retained in the Kidney. 
When one or more of the calculi described in the preced- 
ing section are detained in the infundibula or pelvis of the 
kidney, it frequently happens that they increase in that situa- 
tion 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 beautiful 
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. 
