76 FORMATION OF SHELLS OF ANIMALS, ETC., 
coalescence. Now, as in this case there appears to be 
no reason for assuming the absence of any one of these 
conditions, and as it is certain that, if all the physical and 
chemical means employed in the production of artificial 
calculi are the same in this—the natural process—as in 
the artificial one, the result will be the same also. There 
seems to be no reason why this explanation of the forma- 
tion of these urinary calculi should not be regarded as 
the correct one. Vitality has not been named as having 
had any share in the formation of these natural products. 
Nor, as it has been demonstrated that bodies in all 
respects analogous to these calculi can be formed without 
any possible vital interference, does there appear to be 
any necessity to attribute any part of the formation of 
these urinary deposits to the influence of “ vital forces,” 
or to cell-development. At any rate it is certain, that if 
vitality does contribute anything to their production, 
the fact of the perfect resemblance between these calculi 
and the artificially formed products proves that this con- 
tribution is so small that it might have been altogether dis- 
pensed with. There is one fact connected with this subject, 
which has been regarded by physiologists and histologists 
as furnishing conclusive evidence in proof of the vital 
origin of these and similar natural products, which is 
that of a soft material— animal basis” —being left after 
the decalcification of these products by the action of hydro- 
chloric acid, of the same form, and with markings similar 
to those which these products had before bemg thus 
treated; but as exactly the same effect is produced by a 
like treatment of artificial calculi formed in a solution of 
albumen in the place of gum, this can no longer be con- 
sidered as an infallible test of an organic formation. This 
residuum in the case of the natural products is regarded 
