48 Extrad of Fourcroy and Vauguelin's 
vad which belong ‘to the urinary matter not changed. » It 
was this>matter itis experienced the greateit and .moft 
fingular change by putrefaction ; it was the focus and fubject 
of it; and it gave birth, above all, to the carbonat of ammo- | 
nia which replaced it, and to the acetous acid, which, as 
the phofphoric and the uric, is found faturated by this kind 
of alcali. It appears, therefore, that in order to procure 
more of the phofphat of ammonia, it is of advantage to em- 
ploy putrid urine. 
IX. An attentive and careful examination of the firft 
phenomena of the putrid decompofition cf human urine, pre+ 
fented to us refults as imterefting at leaft as that of urine en- 
tirely decompofed. Thefe refults are connected, above all, 
with the formation of urinary:caleuli, which were one of 
the mioft important objccts of our labour. We were defirous 
of adding to the w dl-known. fact of the exiftence of caleu- 
Jous matter in every kind of urine, anfwers to the followi ing: 
queflions of fo much importance :—W hy are thefe matters — 
more abundant? Why dees a difpofition to calculus exift in 
fome fubjeéts and not in all, though the urine of all contains. 
what may form them? Why are they formed fometimes 
frecdily, and fometimes flowly? What is the caufe of the 
fix-fold variety of the calculous matters, their mixture, and 
interruption? Though we were far from having found a 
folution to all thele gueltions, we have at any rate "been able 
to refolve fome. aS, 
The white prifmatic cryftals, which are depofted on the 
pellicles or the fides of veffels containing urine, do not fhew 
thenrfelves till the liquid becomes ammoniacal. “They increate 
im quantity and bulk for fix or eight days : they. are prifins 
of fix planes, with py ramids having fix faces, which are rea- 
dily difeoyered to he ammoniaco-magnefian phofphat, like 
that often found, under the fparry fori, at the furface of 
white calenli. This fale does not exift, or is not formed, but 
when there is an exeefs of ammonia in the urimary liquor. 
This ammonia, by faturatimg the free phofphorte acid, fepa-~ 
rates the gelatinous matter lich gives birth toa Taucous 
precipitate, and contlitutes with that acid, and by uniting 
itfclf to the phofphat of magnetia, the AMIIMOBLACO- -raagnefia nn 
8 phofphat, 
7 
