DIGESTIVE SYSTEM 



315 



Enamel 



Fir. 151. Lower jaw bone with the teeth in place ; 1, 2, S, molars ; 

 4, 5, bicuspids ; 6, canine ; 7, 8, incisors. 



small aperture at the end of the root, nerves and 

 blood vessels enter this cavity. 



Care of the teeth. Enamel is not a living substance 

 and can not be repaired when injured. Frequently the 

 enamel is cracked or worn through. This may be 

 caused by picking the teeth with a hard instrument 

 such as a pin. A sudden 

 change in temperature is 

 likely to crack enamel. Par- 

 ticles of food sometimes 

 remain between the teeth. 

 These decay and form an 

 acid which destroys the 

 enamel. After this, decay Bone 

 takes place rapidly in the 

 soft dentine. 



A person is always well F\S. 152. section of a tooth. 



entine 



Pulp 

 Cavity 



Blood 

 Vessel 



Cement 



Nerve 



