ear, after this period they fail to do so: they are not
sufficiently numerous,--in their structure they are not strong or
durable,--nor is their power of mastication sufficiently great.

They are not sufficiently large or numerous. If the mouth of a child
at this age is examined, it will be seen, that a considerable interval
has taken place between the teeth in consequence of the growth and
expansion of the face; hence a larger set has become necessary to fill
the arch. But it may be asked, do not the teeth grow with the growth of
the body? and if not, why is it so? They do not, and for this reason:
the important office which these organs are destined to perform requires
that they should be composed of a substance too dense and of too low
an organization to allow of any subsequent growth and enlargement. Thus
the size of the teeth is determined and acquired before they make their
appearance through the gums. This being the case, it will be readily
seen, that the teeth which would be of appropriate size in the mouth of
the infant, would be quite inadequate to the enlarged dimensions of the
adult; hence the necessity of a second set, exceeding in number, and
size the teeth of the first.

That a necessity also exists at this age, that the weak and delicate
teeth of childhood should be exchanged for a set stronger and more
durable in their structure, more robust and more powerful, will be
sufficiently apparent, if we only recollect the great change which has
gradually been taking place in the nature of the food of the two epochs
of childhood and adult age.

The second set, or permanent teeth, then, lying under the milk-teeth
and hidden in the jaw, undergo in this situation their full
developement, before they appear above the gum. This occurrence
commences about seven years of age, at which period the first set
begin to fall out from their roots becoming absorbed, and no longer
retaining their hold of the jaw; to be entirely replaced in the course
of a few years by the permanent set, which thus succeeds them. The
first teeth of this set which make their appearance are the large
double teeth, which emerge from the gum immediately behind the last of
the temporary set. Next the two front teeth of the lower jaw fall out,
and are succeeded by two others of similar character and form, but of
larger size; then the two corresponding teeth of the upper row are cast
off, and their place supplied; shortly after the teeth immediately