a new species of Urinary Calculus . 22$ 
By evaporation to dryness, the acetic acid was removed, 
and by subsequent increase of heat, the sulphate of ammonia, 
and excess of sulphuric acid were expelled. 
The residuum being then dissolved in water, and the liquor 
suffered to crystallize by spontaneous evaporation, there re- 
mained a quantity of sulphate of magnesia, that weighed rather 
more than the quantity of calculus taken for the experiment. 
It was evident, therefore, that in this instance, the calculus 
examined did not consist of super-phosphate of lime, and 
there is some reason to doubt, whether a compound, that is 
so very soluble in water, ever forms a part of urinary con- 
cretions. 
Although the treatment of diseases is not in general, a fit 
subject to occupy the time of this Society, there is nevertheless, 
one suggestion, with respect to the prevention of calculous 
complaints, so nearly connected with my present subject, that 
I think it may deserve to be recorded. 
Since the white matter contained in the urine of birds, 
which is voided along with their dung, has been remarked by 
M. Vauquelin, to consist principally of uric acid, I have paid 
some attention to the different proportion in which this matter 
is voided by different species of birds, to see how far it ac- 
corded with the different qualities of their food. And I found 
that in the dung of the goose, feeding wholly on grass, the 
proportion did not seem so much as of the whole dung. 
In that of a pheasant kept in a cage, and fed on barley alone, 
it was about T '- part. In that of a hen, having the range of 
a garden and farm yard, and consequently procuring insects, 
and possibly other animal food, the proportion was manifestly 
much greater, and combined with lime. In the dung of a 
MDCCCX. H h 
