BACTERIA IN DENTAL CARIES. 393 



infusion) long threads, which break up into short 



segments. 



It is evident, however, that the designation " lepto- The existence 

 thrix " cannot be employed as a generic term, for ihe 

 most various kinds of bacilli may produce these thread- 

 like formations, and the threads which occur in the 

 buccal secretions and in the deposit on the teeth are 

 probably nothing more than the thread form of various 

 well known, or still unknown, and widely distributed 

 bacilli. It is possible, for example, that bacillus 

 butyricus not uncommonly takes part in the formation 

 of leptothrix in the mouth ; it is probable, however, that 

 many other bacilli, more especially anaerobic bacilli, do 

 the same. Since we have been able to work with better 

 microscopes and with staining methods it is easy to 

 convince ourselves, from the marked morphological 

 differences, that the leptothrix threads of the mouth do 

 not belong to one individual species ; the threads show 

 very great variations in thickness, at times they form 

 spores (or the early stages of sporo formation) arranged 

 in a characteristic manner ; some threads are stiff an,d 

 readily broken, others are flexile, &o. . The species of Fruitless 

 bacteria which have as yet been isolated by cultivation 

 from the buccal secretion do not appear to be identical 

 with those bacilli which form the marked threads which forms, 

 have led to the designation leptothrix ; as a matter of 

 fact we only obtain by cultivation a small fraction of the 

 numerous species which we find by the microscope in 

 the secretions of the mouth. Miller also states, in his 

 most recent communication, that the leptothrix 'buccalis 

 has not as yet been cultivated pure. 



As regards the other organisms found in the mouth, Millers 

 Miller has isolated, during the last few years, 25 different 

 species, 12 cocci and 13 rod forms. Some of these have teeth 

 been already mentioned ; we may refer here to the 

 organism described by Miller under the symbol e. 

 This forms small curved bacilli, often S-shaped from the 

 union of two individuals ; it grows on gelatine, and causes 

 its liquefaction, and is probably identical with the spiril- 

 lum of Finkler and Prior. The characteristics of the 



