from the human Bladder. 3 1 1 
Dr. Powel examined its chemical composition, and informs 
me, that it decidedly consists of the triple phosphat of ammo- 
nia and magnesia, with phosphat of lime, forming together 
the fusible calculus of Dr. Wollaston (Phil. Trans. 1797.) 
mixed with a certain portion of animal matter, which was se- 
parated and floated under a membrane-like form, on the 
solution of the salts in diluted acids. That this composition is 
demonstrable by all the usual relations to alkalies and diluted 
acids, and the precipitates from solutions in the latter, by am- 
monia, and also by its fusion into enamel under the blow-pipe, 
and that the general external character of the calculus estab- 
lishes the same fact by its semi-transparent appearance, and 
regular prismatic crystals of the triple salt, discoverable by a 
magnifier, between the more compact layers. 
The nuclei were examined solely with the blow-pipe, from 
a wish not to disturb so fine a specimen beyond what had been 
done by the operation. By this examination they were found 
less fusible than the general mass, and appeared to contain a 
larger proportion of phosphat of lime, for by admixture of a 
portion of triple phosphat of magnesia, taken from another 
part of the same calculus, they were rendered as fusible as 
the rest. 
This calculus accords entirely with the description given by 
Fourcroy (Systeme de Connoisance ^Jheinique), and confirms 
his farther observations on this species. “ Ce sont aussi les 
“ concretions urinaires les plus volumineuses de toutes ; elles 
“ ont depuis le grosseur d’une oeuf jusqu'a une volume qui 
“ occupe toute la vessie, en la distendant meme considerable- 
‘ ment.” From this passage, it should seem that similar in- 
stances had occurred to Monsieur Fourcroy; but from my 
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