32 FORMATION OF SHELLS OF ANIMALS, ETC., 
action, either effectively or imeffectively, upon the mole- 
cules of all bodies. It may now be asked what the 
property conferred by the viscid substance upon the car- 
bonate is, and in what way it acts in producing such an 
effect as that inferred. In answer I may observe, that it 
is not only gum arabic and albumen which act in this 
manner upon the carbonate of lime; glycerine has the 
same effect, and probably all other viscid substances, if 
only they are capable of combining intimately with the 
nascent carbonate. Hence this effect of viscidity may 
depend upon some property of animal or vegetable matter, 
which is no other than a form of attraction peculiar to 
organic products, differing from chemical attraction in 
producing its effects, independently of any chemical change 
in the substances acted upon; as, for instance, when two 
recently exposed surfaces of elastic gum are brought 
together, they unite without any sensible development of 
chemical action, differmg from the attraction of gravi- 
tation in taking place only at insensible distances, and, 
lastly, differmg from that force which acts idiscrimi- 
nately upon all substances, organic and inorganic, called 
cohesion, in possessing in connexion with a certain amount 
of adhesiveness, a degree of elasticity, the two making up 
together the property called viscidity or tenacity, a pro- 
perty occurring only, with the exception of certam com- 
pounds of silica, in substances of animal or vegetable 
origi. Now, as to its action, it may be observed that if 
this power of attraction still continues to be exerted 
between the ultimate molecules of this class of substances, 
after their union with the carbonate of lime, as was 
exerted by visible portions or large masses of these sub- 
stances when uncombined, it is perfectly conceivable that 
such a union would affect the repulsive or separating 
