On the Differences in the Structure of Calculi. 173 



monia depends in all instances upon the decomposition of the 

 ammoniacal salts contained in the calculus, more especially 

 of the ammoniaco-magnesian phosphate, and that no sub- 

 stance which can be called urate of ammonia exists in calculi. 

 The mulberry calculus (oxalate of lime) I have but rarely 

 met with. In those preserved in the Hunterian collection, 

 there is a large relative proportion of phosphate of lime, and 

 of uric acid. The purest of them afforded 



Grains. 



Oxalate of lime - 65* 



Uric acid - - 16' 



Phosphate of lime - \5 m 



Loss in animal matter 4 - 



100- 



When calculi of the urinary bladder increase to a very larg^ 

 size, they are generally composed of two or even three of the 

 abovementioned varieties, the ammoniaco-magnesian phos- 

 phate being situated externally, and in the greatest abundance. 



The largest calculus which I have seen, weighed, when 

 recently removed from the bladder, twenty-three ounces and 

 twenty-six grains. It consisted of a large mulberry or oxa- 

 late of lime calculus, the nucleus of which was uric acid, 

 surrounded by a considerable quantity of the ammoniaco- 

 magnesian phosphate in a very pure state. 



Another verv large calculus, weighing fifteen ounces and 

 a half, consisted of a nucleus of uric acid, enveloped in the 

 ammoniaco*magnesian phosphate, not however pure, but 

 intersected by several laminae of uric acid. 



Four distinct substances are extremely rare in calculi ' I 

 have seen one in which the uric acid, the ammoniaco-mag- 

 nesian phosphate, the phosphate of lime, and the oxalate of 

 lime, were all in perfectly separate and distinct layers. 



Four calculi, having the following extraneous substances 

 for their nuclei, were examined. 



1. A common garden pea. 



2. A needle. 



3. A hazel nut. 



4. A part of a common bougie. 



In the two first instances, the calculous depositions were 



of 



