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 



