470 THE HUMAN BODY 



of the teeth and so gain foothold within the tooth substance itself, 

 and we have under way the too-familiar process of tooth decay. 

 Good teeth are so important for efficient mastication, as well as 

 for the appearance of the face, that no pains should be spared to 

 preserve them. Evidently the way to do this is to prevent the 

 accumulation of bacteria in the spaces between them. Thorough 

 cleaning, desirably after each meal, with the occasional use of an 

 antiseptic mouth-wash is fairly but not completely satisfactory. 

 Half yearly inspection and cleaning by a dentist are usually neces- 

 sary to supplement one's own efforts, because of the practical 

 impossibility of keeping every one of the small mouth spaces clear. 

 Such inspection also insures the discovery of decay while the cavi- 

 ties are still small, and makes possible the preservation of the 

 teeth in approximately normal condition for many years. 



Recently evidence has been advanced showing that the saliva 

 varies slightly in alkalinity in different people, and that the sus- 

 ceptibility of the teeth to decay depends largely on the degree of 

 alkalinity. Three general groupings are suggested. Those who 

 fall within the limits of the first group are likely to have perfect 

 teeth even though no care is taken of them. The second group 

 can have good teeth by the exercise of reasonable care. The third 

 group have difficulty in preserving the teeth in good condition 

 in spite of unremitting attention to them. This observation ex- 

 plains the frequent, occurrence of perfect teeth in savages and 

 others who never pay them the slightest attention, and the prev- 

 alence of decay among the most highly civilized. It is probable, 

 although not proven, that the nature of the diet has much to do 

 with the degree of alkalinity of the saliva. 



Of late years a great deal of attention has been paid to indirect 

 harm that may follow neglect of the teeth. Allowing colonies of 

 bacteria to flourish among them undisturbed means, of course, 

 that any toxins these may produce will be absorbed into the sys- 

 tem. The result of continuous absorption of such toxins is often 

 manifested in lowering of the general health. Specifically, acute 

 rheumatism is said frequently to follow. 



Deglutition. A mouthful of solid food is broken up by the 

 teeth, and rolled about the mouth by the tongue, until it is thor- 

 oughly mixed with saliva and made into a soft pasty mass. This 

 mass is sent on from the mouth to the stomach by the process of 



