160 Physiology. 



mended by a reliable dentist, is not used, a good white 

 castile soap will serve well. It is better to use tepid water. 

 Toothpicks are useful in removing the larger particles. 

 Quill toothpicks are best; metal should never be used. 

 The teeth should be examined twice a year by a dentist, 

 and .any cavities promptly filled. 



Cause of Decay of Teeth. If the teeth are not thoroughly 

 cleaned the particles of food which remain will soon begin 

 to decay. This decay is caused by the growth of germs, 

 usually some kind of bacteria, and the decay thus begun 

 is likely to develop acids which attack the limy material 

 of which the teeth are composed. When it is necessary 

 to take acid medicines, care should be taken not to let 

 them come in contact with the teeth. Sweet substances 

 are very likely to decompose and form acids ; so we must 

 clean the teeth after eating candies. When the teeth are 

 neglected, a limy substance, called tartar, forms on them 

 and encourages decay. 



The Salivary Glands. The salivary glands make the 

 saliva and pour it into the mouth. There are three pairs 

 of salivary glands the parotid, just back of the angle of 

 the jaw, under the ear ; its duct opens on the inside of the 

 cheek opposite the second molar of the upper jaw. The 

 submaxillary gland lies under the angle of the jaw ; its 

 duct opens under the tongue near the front of the mouth. 

 The sublingual gland is in front of the submaxillary and 

 empties under the tongue (see Fig. 74). 



Salivary Ducts in our Mouths. If the inside of one's cheek be 

 examined by the use of a hand mirror, the opening of the duct from the 

 parotid gland may be seen opposite the second molar of the upper jaw. 

 It usually looks like a pink and white spot, resembling a wound of a 

 bee sting. Sometimes saliva may be seen issuing from it. 



