556 On the Biffere7iees in tlie Structure of Calculi. 



much less liable to a return of the complaint, than where 

 uric calculi have been voided. \ 



In some rare instances we meet with calculi of the bladder 

 which are destitute of uric acid and of oxalate of lime, the 

 nucleus being composed of a little loosely agglutinated am- 

 uioniaco-magnesian phosphate, and the whole calculus con- 

 sisting of that substance, with variable portions of phosphate 

 of lime: in two cases I have met with calculi of this kind, 

 composed of the triple phosphate only : they seem to be en- 

 tirely formed in the bladder. 



Having taken this short view of the formation of calculi, 

 I shall now inquire into the action of solvents, employed 

 either with a view of effecting their solution, or of prevent- 

 ing their formation and increase. 



Solvents are of two kinds. 



]. Alkaline. 2. Acid. 



In the exhibition of these, the practitioner is usually 

 guided by the chemical composition of the calculous matter 

 Toided by urine. 



The different kinds of gravel voided by persons labouring 

 under calculous complaints, may be classed in two divisions. 



1. Uric acid, either in a pure state, or with a very small 

 proportion of the phosphates. 



2. The phosphates t either pure, or with a small propor- 

 tion of uric acid. 



The first species, which generally appears in the form of 

 minute crystalline grains, of a reddish brown colour, or of aa 

 impalpable brown powder, is either entirely soluble in pure 

 alkaline solutions, not emitting an ammouiacal odour, ia 

 which case it consists of pure uric acid: or it does emit an 

 animoniacal odour, and is not entirely soluble, in which case 

 it contains the triple phosphate of ammonia and magnesia. 



When this substance is observed in the urine, the alkalis 

 are recommended. They are exhibited either in a pure state, 

 or as carbonates, and in each instance the uric sediment ge- 

 nerally diminishes rapidly, and during the continued use >of 

 aJkaJine medicines, occasionally disappears altogether. 



\i U;>wever frequently happen* that the matter, voided is 



not 



