if© On the Differences in the Structure of Calculi. 



4. Those formed upon extraneous bodies introduced into 

 the bladder. 



They were arranged under the following divisions. 



1. Calculi, which from their external appearance consist 

 chiefly of uric acid. 



These calculi vary in colour from a deep reddish brown, 

 to a pale yellowish brown. 



They are either entirely soluble in a solution of pure pot- 

 ash, or nearly so. 



During their solution they frequently emit the odour of 

 ammonia. 



When acetic acid is added to their alkaline solution, a pre- 

 cipitate possessing the properties of uric acid is obtained. 



2. Calculi, composed chiefly of the ammoniaco-magnesian 

 phosphate, or of phosphate of lime, or of mixtures of the two. 



These calculi are externally of a whiter appearance than 

 the former. 



Some perfectly white, others gray, occasionally exhibiting 

 small prismatic crystals upon their surface; others again soft 

 and friable, a good deal resembling chalk. They are further 

 characterized by their solubility in dilute muriatic acid. 



3. Calculi, containing oxalate of lime j commonly called 

 mulberry calculi. 



These are distinguished by the difficulty with which they 

 dissolve in dilute acids, by their hardness, and by leaving 

 pure lime, when exposed to the action of the blowpipe. 



Jn the examination of these calculi, I was struck with the 

 small number of those strictly belonging to the first division, 

 having been led, from the account of Fourcroy and Vau- 

 quelin*, and the experiments of Dr. Pearson f 5 to believe 

 that calculi composed of pure uric acid were by no means 

 unfrequent. 



The greater number of the calculi examined by the former 

 chemists, are stated to be completely soluble in the fixed al- 

 kaline leys ; and of three hundred examined by Dr. Pearson^ 

 a large proportion is said to consist of uric acid. 



• Annales de Chimie, xxxii. p. 218. 



$ Philosophical Transactions for 1798, p. 37. 



The 



