94 SCIENCE OF IJOME AND COMMUNITY 



be removed by means of toothpicks or dental floss, but the 

 smaller, tiny particles require the use of a toothbrush. The 

 best time to brush the teeth, if it is done but once a day, is 

 after the evening meal. Otherwise the food particles would 

 remain in the teeth during all the night, thus allowing a long 

 time for the action of the bacteria in producing decay. But 

 while the teeth should be cleaned at least once a day, the 

 best care requires another cleansing after the morning meal. 

 The value of a toothpowder lies in the fact that it contains 

 substances which help to neutralize the acids that cause 

 decay, and it also acts as an antiseptic on the bacteria. 



Sources 'of food. All of our food is made either directly 

 or indirectly by the action of plants. Some of our food 

 consists of the flesh of animals, but these animals have fed 

 on plant food, so that this brings us back to plants as the 

 final source of our food. Starch is made by the green matter 

 in plants known as chlorophyll, generally found in the leaf. 

 This chlorophyll takes water and carbon dioxid, and from 

 this, in the presence of light, manufactures starch. The 

 water comes up from the roots through the stem and the 

 carbon dioxid passes from the air through small openings 

 in the leaf. This starch is one of our commonest foods. 

 Later, some of this starch is united in the plant with sub- 

 stances that come up through the roots from the soil, and by 

 this process proteins are formed, which constitute, as we 

 have seen, another important food for mankind. 



Summary. The whole matter of the hygiene of foods 

 may be briefly summarized by saying that a thorough masti- 

 cation of foods will help develop a natural appetite, which 

 will decide for us both what to eat and how much to eat. 

 One should also occasionally compare his weight with that 

 of the average for his height ; and compare his daily diet 

 with standards that have been set as a result of experiments, 

 so that he may know whether he is approximating these 

 standards. As general guides these suggestions may be 



