140 



BACTERIA IN RELATION TO DISEASE 



at culture, and therefore the biochemical characters of the different species 

 are unknown. This much, however, has been discovered, that the various 

 kinds present, feeding upon the food particles remaining between the teeth, 

 produce lactic and other acids, by which the enamel is decalcified in places. 

 A path to the interior tissues of the tooth being now open, the bacteria 

 bore their way, by means of their acid secretions, deep into the dentinal 

 tubules, just as a lichen eats into stones. The organic substance of the 

 tooth also is destroyed and the tooth becomes hollow and rotten. The 

 following figures illustrate the effect upon the dental tissues : 



Total Weight. Lime. 



187-2 cubic millimetres healthy dentine. . . 0-36 gr. 0-26 gr. = 72% 

 187-2 cubic millimetres carious dentine . . . 0-08 gr. 0-02 gr. = 26% 



Loss . 



Organic Matter. 

 o-i gr.-28% 



0-28 gr. 0-24 gr. 



0-04 gr. 



Thus the loss of calcium salts by 

 the teeth caused by the acid secre- 

 tion of the bacteria is 92 per cent., 

 that of the organic substance 40 

 per cent. 



Dental caries can hardly be 

 looked upon as a ' disease ' ; it is 

 rather the necessary consequence, 

 sooner or later, of the action of 

 micro-organisms that are normal 

 inhabitants of the buccal cavity 

 introduced daily with the food. 

 The destruction of the teeth is not 

 the work of any one species in 

 particular, but due to the activity 

 of several kinds. 



Whence the bacteria of the 

 mouth come is not at present 

 known. The typical B. buccalis 

 maximus is not found outside the 

 body, and attempts at culture 

 have been unsuccessful. 



The discovery of bacteria, 



indistinguishable from those of our own mouths, in the hollow teeth of 

 Egyptian mummies shows that these micro-organisms have been our 

 companions from the earliest times. 



The healthy stomach is, in consequence of the acidity of the gastric 

 juice, not suitable for the development of a local bacterial flora. If however, 

 as a result of illness or disease, the secretion becomes less acid or neutral, 



FIG. 26. Bacteria of the mouth and teetli. a, mass of 

 mixed forms (from Miller); 6, dentinal tubules filled and 

 widened by bacteria, partly cocci, partly rods (from Miller) ; 

 c, Spirillum sputigenum ; d, Bacillus maximus buccalis, 

 shows granulose reaction ; e, cocci ; f, Spirochaete den- 

 Hunt; g, Vibrio buccalis ; k, rods, probably lactic acid 

 bacteria (B. acidi lactici). Magn. a about 250, b 400, c-h 

 about 1 200. 



