432 BIOLOGY FOR BEGINNERS 



Hygiene of the Teeth. The importance of dental hygiene has 

 been mentioned before but cannot be too much emphasized. 

 Conditions in the mouth are ideal for the growth of bacteria which 

 cause decay. Warmth and moisture are sure to be present, and 

 unless great care is observed, particles of food will remain for the 

 bacteria to feed upon. 



It is not a pleasant experiment, but if the teeth be scraped with 

 the finger nail and the odor of the substance removed observed, 

 we will have no doubt that decay is going on. The total area of 

 possible tooth infection is equal to that of two standard petri 

 dishes (over twelve square inches). 



The decay of food between the teeth destroys the protective 

 enamel and the dentine then goes rapidly. The immediate re- 

 sults are bad breath, pain, and loss of teeth. Fully as serious are 

 the secondary consequences of poor chewing: indigestion, pus 

 diseases from infected gums, rheumatism, and nervous disorders. 

 Tonsils, throat, ears, and even the lungs may be infected from the 

 teeth. 



The first or " milk teeth " deserve as great care as the permanent 

 set. If they decay and are removed too soon the jaws and face 

 never attain their proper shape and proportion, and the later teeth 

 will not fit properly together. 



Hygiene of the Feet. With the possible exception of the eye, 

 no human organ has been worse abused than the foot. We crowd 

 our feet into air-tight leather boxes, bend the toes together, lift the 

 heel high off the ground and then wonder why we suffer from 

 corns, bunions, and fallen arches. Proper shoes should have their 

 inner edges nearly straight, heel low and broad, toe with room 

 enough so that the toes can separate and " wiggle." The uppers 

 should be flexible, as porous as possible, and not too tightly laced. 

 The arch of a normal bare foot should not touch the floor on the 

 inner edge and the shoe should be so shaped as to support this up- 

 ward curve. The selection of shoes should be guided by the ex- 

 pert advice of a doctor or trained fitter and not be governed by the 

 vagaries of style or the demands of fashion. Feet were made to 

 walk on, not to look at. In walking the feet should be carried 



