URINARY CALCULI. 
which is so frequently emitted by persons, threatened 
with the stone, consists always of this acid. As oxalic 
acid does not exist in urine, some morbid change must 
take place in the urine when calculi composed of oxalat 
of lime are deposited. Brugnatelli’s discovery of the 
instantaneous conversion of uric acid into oxalic acid 
by oxy-muriatic acid, which has been confirmed by the 
experiments of Fourcroy and Vauquelin, throws consi 
derable light upon the formation of oxalic acid in urine, 
by shewing us that uric acid is probably the basis of it; 
but in what manner the change is actually produced, it 
is not so easy to say. 
As our ignorance of the cause of urinary concretions 
puts it out of our power to prevent their formation, 
the ingenuity of physicians has been employed in at 
tempting to discover substances capable of dissolving 
them after they have formed, and thus to relieve the 
human race from one of the most dreadful diseases to 
which it is subject. These attempts must have been 
vain, or their success must have entirely depended up 
on chance, till the properties of the concretions them 
selves had been discovered, and the substances capable 
of dissolving them ascertained by experiment. I shall 
therefore pass over the numerous lithanthriptics which 
have been recommended in all ages, and satisfy myself 
with giving an account of the experiments made by 
Fourcroy and Vauquelin to dissolve stones by injections 
through the urethra, made after their analysis of the 
urinary calculi. 
The component parts of urinary calculi, as far as sol 
vents are concerned, may be reduced under three heads: 
1. Uric acid and urat of ammonia; 2. The phosphats; 
3. Oxalat of lime. 
459 
Chap. II. 
Attempts 
to discover 
a solvent of 
calculi.