124 
CYSTIC CALCULUS IN THE HORSE. 
Analysis . — A fragment being subjected to heat on a piece 
of platinum foil, emitted, first, a urinous smell, and afterwards, 
as it blackened, the odour of animal matter was given off. The 
flame being urged by means of the blow-pipe, the mass 
became white, and lost about half its weight. This being 
dissolved in dilute hydrochloric acid, the oxalate of ammonia 
threw dov'n an abundant white precipitate; but water of 
ammonia yielded none. 
A few grains being placed in a test-tube, and hydrochloric 
acid poured over them, they underwent solution with con- 
siderable effervescence, leaving abundant flocculi. 
The composition, therefore, is, carbonate of lime and 
animal matter ; this last being, probably, mucus. 
Remarks. — It would seem that the existence of a calculus 
composed w-holly of carbonate of lime is rare in the human 
subject, as Professor Brande states that, among several hun- 
dred calculi which he has examined, he has never met with 
one, although he has seen many beautiful specimens taken 
from other animals. 
From the urine of all the herbivora it is well know r n that 
a deposition of carbonate of lime is of constant occurrence, 
and especially so from that of the horse. <e When examined 
by the microscope, after being washed with water, the par- 
ticles of this carbonate are found to be small transparent 
spheres, like globules of glass, and strongly refracting light. 
Allowed to dry, and examined after immersion in Canada 
balsam, their structure is beautifully distinct, each sphere 
being made up of myriads of minute needles, radiating from 
a common centre. With polarised light, these interesting 
objects present a series of concentric coloured rings, tra- 
versed by a black cross.” — Dr. Golding Bird. 
The formation of this deposit is owing to a metamorphosis 
that takes place in the urea, by which it becomes converted 
into carbonate of ammonia, through the assimilation of 
water with its elements ; and this being acted on by the 
soluble lime salts, separated from the blood by the kidneys, 
an insoluble carbonate of lime is thrown down. 
1 atom Urea . . . = C 2 H 4 N 2 0 2 
2 atoms Water . . . = H 2 0 2 
2 atoms Carbonate Ammonia = C 2 II 6 N 2 0 4 
A diseased condition of the mucous lining of either the 
pelvis, of the kidney, or of the bladder, is necessary to effect 
this change, the action being purely catalytic ; and when 
once this disease of the mucous membrane is set up, the 
ammoniacal urine becomes a constant irritant, andgives rise 
