150 THE LACTATES, AND UREA AS IT EXISTS IN URINE. 
acid has been recognised in most of the secretions and fluids 
of animals. It exists in the blood, milk, bile, saliva, sweat, 
synovia, and urine, when in a healthy state. We cannot, 
therefore, mistake the importance of this acid in the animal 
economy, especially when we remark that it disappears under 
the influence of certain morbid causes, as soon as the secre- 
tions alter, thicken, coagulate, and then calculi and divers con- 
cretions appear, formed, for the most part, of earthy and alka- 
line phosphates. But these phosphates are very soluble in 
lactic acid, a marked circumstance which very naturally ex- 
plains the formation of the phosphatic calculi, and exhibits the 
necessity of the presence of lactic acid in the organic fluids. 
Prepossessed with the idea of restoring to the urinary ap- 
paratus the two principles of which they are deprived in cer- 
tain affections, we endeavored to combine artificially the lac- 
tic acid and the urea. We accomplished this in a complete 
manner by double decomposition, and obtained, after nume- 
rous trials, a lactate of urea , crystallized in fine prismatic nee- 
dles of extreme purity, and great whiteness. 
But has not this preparation its analogue in the animal eco- 
nomy ? was now the question to be asked, and of which we 
did not hesitate to attempt the solution. 
When we desire to obtain the urea contained in urine, we 
concentrate this liquid to seven-eighths. There is then depo- 
sited a large quantity of salts formed principally of chlorides, 
alkaline sulphates, calcareous and ammoniaco-magnesian phos- 
phates. If we separate this mass by the filter, there is ob- 
tained a very acid, brown liquor, in which alcohol of 40°causes 
the formation of small crystalline, acid, hygrometric grains, 
which, purified by carbon, become prismatic crystals, which 
are deliquescent, of a sharp taste, and redden litmus. If these 
crystals are treated with hydrate of zinc and alcohol of 36°, 
there is obtained, on the one hand, a lactate of zinc, and on 
the other, by evaporating the alcoholic solution, a very pure 
urea, not hygrometric, and possessing all the properties which 
characterize this body. It is then evident that the crystal- 
line grains, obtained by the simple evaporation of urine pre- 
