in the Structure of Calculi . 
22 J 
Grs. 
Uric acid 
Animal matter 
4-5 
2 5 
7.0 
This is the largest proportion of animal matter which 
I have met with. 
A small calculus from the kidney, weighing 3.7 grains, 
afforded by a like treatment 3.5 grains of uric acid, so that it 
was nearly a pure specimen of that substance. 
The largest calculus of this kind which I have examined 
weighed seventeen grains ; much larger ones have been 
found, but there is no evidence of their not having remained 
in the urinary passages for some considerable time. Thus 
Dr. Heberden mentions one weighing twenty-eight grains.* 
It often happens that the ingredients are not united toge- 
ther so as to form a calculus, but are voided in the state of a 
fine powder, commonly termed sand. This consists either 
of uric acid, or of the ammoniaco-magnesian phosphate, alone, 
or with the phosphate of lime. 
I am induced to believe that the last mentioned substances, 
although the production of the kidnies, and held in solution, 
are never met with in a separate state till the urine has been 
at rest, and therefore, calculi from the kidnies are never com- 
posed of the phosphates. 
In a few instances, calculi from the kidnies, composed of 
oxalate of lime, are voided ; but this is a very rare occurrence : 
of three preserved in the Hunterian Collection, two are 
* Comment, on the Hist, and Cure of Diseases, 3d. edit. p. 88. 
MDCCCVIII. G g 
