as indicative of the Age of the Animal. 
313 
and produce an absorption of these projections, with, of necessity, 
a daily diminishing firmness of tlieir attachment to the jaw. 
It is hardly necessary to enter at any length into an explanation 
of the manner in which the absorption of a tooth is effected. 
Pressure is its great promoter. The permanent tooth imbedded in 
tr.e socket, interferes more or less, by its pressure upon the pulp, 
with the nutrition of the temporary tooth, and thus predisposes 
its elementary matters to undergo a change. Besides this the 
temporary tooth having served its purpose, the balance of nutrition 
is turned against it. On the other hand, the developing process 
is steadily going on in the permanent tooth, and thus its power 
as an expeller daily increases. 
Absorption necessarily implies previous solution, but how 
the solid parts of a tooth, or indeed of any part of the body, 
become fluid, is not well understood. With the theories of 
this change we have nothing to do. It appears that in propor- 
tion to the quantity of the animal matter in the several structures 
of a tooth, so is the rapidity of their absorption : thus Crusta 
is observed to give way quicker than Dentine, and Dentine 
quicker than the Enamel. This difference in the rate of the 
absorption of the constituents is well seen on a close inspection 
of the crowns of the temporary teeth which have fallen from 
absorption. An advantage arises from this : the enamel which 
covers the tooth will be found to project from the edges, and thus 
to hold its connexion with the gum when the whole of the middle 
part of the tooth has been hollowed out as if with a chisel. 
Premature removal is thus very often prevented. 
Tlie influence of absorption over the fall of the temporary 
teeth will necessarily be in proportion as the pressure to their 
fangs is direct. In the horse and pig the permanent incisors come 
up more within the original sockets of the temporary than in 
the ox or sheep, and this seems to be of itself almost sufficient 
to produce the removal of the temporary teeth of those animals. 
In the ox and sheep, on the contrary, from the disproportion 
which exists in the size of the two kinds of teeth, and also from 
the greater readiness with which the surrounding bone gives way 
to the pressure, it generally happens that the permanent incisors 
come up rather without than within the sockets which are occupied 
by the temporary. The temporary teeth are therefore very often 
pushed aside instead of being expelled. The liability to this dis- 
placement is increased by the loose connexion which at this time 
exists between these teeth and their sockets. These several cir- 
cumstances now and then lead to a persistency of the temporary 
incisors, by their retaining a hold of the surrounding paits. An 
instance of this kind is exhibited in the following engraving, 
fig. 21, where we observe that the second pair of temporary 
