DEVELOPMENT OF TEETH. 
167 
root of the tooth is developed, the crown is gradually pushed 
upwards, so as to press against the upper portion of the 
capsule and the gum by which this is covered. These 
parts yield slowly to the pressure ; and the tooth makes its 
way to the surface ; or, in common language, is cut. 
175. The process of “cutting teeth” is usually not a severe 
one in the healthy and well-managed infant; but it occasions 
the death of vast numbers of children who are injudiciously 
treated; and it is especially fatal to those who have a ten¬ 
dency to disease of the nervous system. The irritation 
caused by the pressure of the tooth against the gum, is 
liable to excite, in such cases, convulsive actions of various 
kinds, on the principles hereafter to be explained (§ 473); 
and, as the removal of the source of irritation is of the 
most urgent importance, the lancing of the gums,—doing 
that in an instant which the pressure of the tooth might not 
accomplish for days,—is a measure of most obvious utility; 
however unnecessary it may seem, in ordinary cases, to in¬ 
terfere with the course of nature. But it is of the utmost 
importance at the same time to bring the nervous system into 
a less excitable condition ; and no measure is commonly more 
efficacious in this respect, than removal into a fresh and pure 
atmosphere. 
176. At the same time that the development of the tooth 
is thus taking place, the bone of the jaw is becoming hardened, 
and closes round its root, forming a complete socket. This 
partly interrupts the passage of vessels and nerves to the 
tooth, which, when once fully formed, seems to acquire no 
further growth, and to possess but little power of repairing 
injuries occasioned by disease or accident. Hence a tooth 
which is broken or decayed, is not restored as a bone would 
be. Still, however, its root or fang is penetrated by a small 
nerve and artery, which are distributed to the membrane 
that lines the cavity ; and it is to the action of air upon the 
former, when the cavity is laid open by decay, that the pain 
of tooth-ache is chiefly due. The remedies which are most 
effectual in removing this pain, such as kreosote, nitric acid, 
or a heated wire, are those which destroy the vital power of 
the nerve. 
177. But there are teeth, in many animals, which never 
cease to grow, and in which the central cavity is always filled 
