SYSTEMATIC SYNTHESIS OF TISSUES INTO ORGANS. 341 



Remark. The jaw does not always expand as rapidly as teeth ap- 

 pear, whence they must be irregular and crowd upon each other. This 

 defect can be corrected by pressure on the teeth when age has expanded 

 the jaw ; or, if it does not expand the jaw sufficiently, a tooth can be 

 extracted and the others regulated. 



FIG. 227. 



1002. A TOOTH IS DIVISIBLE into 



the Crown, or exposed part, the neck, 

 or part covered by gum, and the fang, 

 or part buried in the socket. 



1003. A SECTION OF A TOOTH 



(Fig. 227) SHOWS that it is construct- 

 ed of the ivory or dentine body, 2, 

 covered with the hard, polished 

 enamel, 1, and the softer cement, 4. 

 The body contains a considerable 

 quantity of pulp, in which are nu- 

 merous blood-vessels and nerves, 

 that enter by the minute channels in the fang. 

 Fig. 50.) 



1 004. TEETH DECAY because constructed of improper 

 material, that will not bear necessary exposure, or be- 

 cause the enamel is cracked or worn through, exposing 

 the ivory, or because tartar is allowed to collect about 

 the gums and become deposited between them and the 

 teeth. 



1005. Remark. As THE TEETH ARE FORMED IN INFANCY and youth, 

 it is of exceeding importance that wholesome food should be taken and 

 general health maintained during that period. 



1006. Illus. IF A CHILD HAS A FEVER DURING CONSIDERABLE TIME, 



the teeth growing at that time will manifest a ridged appearance. 



1007. Remark. FROM THE KNOWN EFFECTS OF HEAT AND COLD, suc- 

 cessively applied to similar substances, it would be expected that any- 

 thing hot or cold, acting on the enamel, would have a tendency to crack 

 it; and sometimes it looks like a glaze-cracked piece of earthenware. 



1008. Illus. HOT WATER AFTER COLD, OR COLD WATER AFTER HOT, 



poured into a tumbler, will crack it. 



1002. How is ? 1003. What does ? 1004. Why do ? 1005. what fol- 

 lows ? 1006. What effect ? 1007. Whut inference ? 1008. What effect of ? 



