BACTERIA IN DENTAL CARIES. 391 



rarely that, at its uppermost part, the growth is some- 

 what broader. Older cultivations have a distinct smell 

 of herring brine. It was frequently found by Leube in 

 old urine. The bacilli are able to convert urea into 

 carbonate of ammonia, and they do this more energetically 

 ihan the micrococcus urese. 



Leube was able to demonstrate a similar energetic Other bacilli 

 dehydrating action on urea in the case of two other ^fiar &otior 

 bacilli, and also of a species of sarcina. The first 

 bacillus formed thick oval rods, 1*2 to 1*5 /*. in length, 

 and *7 to *8 p. in thickness ; on gelatine they form 

 superficial dull grey colonies with sharp margins, which 

 descend rapidly to the level of the nutrient soil, their 

 marginal zone being narrow, transparent, and finely 

 granular. The second bacillus was 1*2 to 1'4 p. in 

 length, *6 /x. in breadth', had sharply truncated ends, 

 and formed circular, highly refracting, fairly high 

 colonies, of a pale greyish-yellow colour, and tough 

 consistence. 



Bacteria in Dental Caries. 



The numerous organisms which are constantly present 

 in the secretions of the mouth and in the deposit on the 

 tongue and teeth, set up in part very various fermenta- 

 tive and putrefactive processes, and in part they play a 

 role in the etiology of dental caries. According to Miller Etiology of 

 the . first stage of dental caries consists in a decalcifica- dental caries. 

 tion of the dental tissue by acids, these being chiefly 

 forme^ in the mouth by a process of fermentation ; and 

 the second stage must be regarded as a simple destruc- . 

 tion of the softened tissue of the tooth by micro- 

 organisms. 



Formerly the most important role in these processes Leptothrix 

 was ascribed to a particular genus the leptothrix 

 which were defined as long thin threads, *7 to 1 p. in 

 breadth, apparently without any segmentation and often 

 united in dense bundles or felt-like masses ; the forms 

 which occur in the buccal cavity mixed with micrococci and 

 other fission fungi, were designated leptothrix buccalis. 



