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XIII. On Cystic Oxide , a new species of Urinary Calculus. 
By William Hyde Wollaston, M.D. Sec.R.S. 
Read July 5, 1810. 
The principal design of the present essay is to make known 
the existence, and to describe the leading properties of a new 
species of urinary calculus from the human bladder ; but I 
shall at the same time take the opportunity of correcting an 
inaccuracy or two that I have observed in my former com- 
munication on this subject. (Phil. Trans. 1 797.) 
I, on that occasion, took notice of five kinds of urinary 
calculi, 
1. The lithic acid, since called uric acid, originally analysed 
by Scheele. 
2. The oxalate of lime, or mulberry calculus . 
5. The phosphate of lime, or bone-earth calculus. 
4, The ammoniacal phosphate of magnesia. 
5. The fusible calculus , which consists of the two last spe- 
cies combined. 
It is now about five years since I first met with another 
species, evidently differing from each of those before described* 
It was in the possession of Dr. Reeve of Norwich, who 
obligingly gave me a portion of it for the purpose of examin- 
ing its chemical qualities. It had been taken from his brother 
when he was five years old, and at that time was covered 
with a coating of phosphate of lime very loose in its texture, 
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