48 
Rainey, on Artificial Calculi. 
These calculi are very large, being -J^tli or g^oth of an inch 
in diameter, and spherical, excepting sometimes on the side 
which was in contact with the glass, which is flattened. 
They are beautifully laminated, and coalesce in the same 
manner as those before described. When treated with weak 
acetic acid they effervesce, and leave a residue of amorphous 
matter. When dried they retain their globular figure, but 
have not the smooth and glassy appearance of those formed 
on the slides. Under polarized light they present a cross and 
appear somewhat coloured, but do not exhibit the prismatic 
colours. They cannot be preserved in any fluid, as they 
suflPer disintegration and gradually disappear. Even if they 
are put up in a cell with the solution of gum in which they 
were formed, still they gradually, though only partially, 
suffer disintegration. All the carbonate of lime disappears, 
but a residue is left having the same laminated appearance 
(though seen very faintly) as the original calculus, but this 
residue is not in the least visible by polarized light. These 
peculiarities are, I have no doubt, due to the presence of a 
quantity of insoluble vegetable matter intimately mixed with 
the particles of carbonate, which prevents that complete coa- 
lescence which otherwise would have taken place ; and hence 
in these calculi the molecules are kept together with but a 
very feeble cohesive attraction, as is indicated by the absence 
of that degree of transparency which characterises the other 
forms of artificial calculi when perfectly dry. Hence it is 
probable that the force which keeps these heterogenous par- 
ticles together is chiefiy, if not entirely, the attraction of 
gravitation. Consequently when they are removed from the 
bottle in which they were formed, where all the molecules 
entering into the structure of each of them would have been 
exactly balanced between the mutual attraction of the mole- 
cules themselves, and that exerted upon them by the various 
part of the bottle, to a small cell of glass where they will be 
brought into much closer contiguity with surrounding ob- 
jects, this balance will be destroyed, and the molecules, 
being now attracted by surrounding substances more forcibly 
than by one another, their separation will ensue. The vegetable 
matter molecularly united with the carbonate of lime being 
very light, and probably having a slight cohesive attraction 
existing between its own particles, will retain its place, 
whilst the particles of carbonate will become attached to the 
sides of the cell. I consider that there is nothing wonder- 
ful either in the facts here stated respecting these calculi, or 
in the explanation of them here advanced. It is only just 
what might have been anticipated under such circumstances. 
