270 !'• H. KEYES AND II. V. JORDAN 



combination of penicillin and a concomitant change in diet will 

 abrupth' arrest caries in the teeth, it does not always depress the 

 cariogenic microbiota so completely that offspring are caries-inactive 

 when tested ( Keyes and Fitzgerald, 1963 ) . 



The implications of experimental caries transmissibilitv have not 

 been readilv understood. Probably the most important implication 

 of caries transmission is that conventional laboratory animals, nota- 

 bly hamsters, can be obtained which harbor a negligible number of 

 cariogenic microorganisms. Such animals can be used in the design 

 of a "normar" experimental model for studying biological interac- 

 tions associated with caries. See Fig. 4. The procedure involves less 

 complicated technics than the gnotobiotic ones, and the methods are 

 within reach of almost anv laboratory Investigators have a method 

 for studving caries in conventional animals which is not basically 

 different from those used in the studies of other experimental infec- 

 tions, e.g. tuberculosis (Ratcliffe and Palladino, 1953). 



Manv attempts have been made to induce experimental caries by 

 an inoculation of organisms thought to have a cariogenic potential 

 (Etchells and Devereux, 1932-1933; Rosebury et al, 1934; Belding 

 and Belding, 1943; and others). However, unequivocal results were 

 not obtained before the use of the previouslv discussed gnotobiotic 

 technics (Orland et al, 1955; Fitzgerald et al, 1960). 



It has been interesting to find that dental caries can be induced by 

 an inoculation of pure cultures of certain organisms isolated from 

 the mouth of caries-active hamsters (Fitzgerald and Keyes, 1960, 

 1963). Rampant coronal caries has onlv followed the inoculation of 

 specific strains of hamster streptococci in association with the proper 

 diet. See Fig. 5. It has not followed the inoculation of various other 

 strains of acidogenic streptococci isolated from the mouths of either 

 caries-free hamsters or caries-active rats, nor the inoculation of lacto- 

 bacilli and numerous other acidogenic and non-acidogenic organ- 

 isms; i.e., coronal caries has not been induced bv inoculations of 15 

 strains of fecal and oral streptococci, lactobacilli, and diphtheroids, 

 and 5 strains of acido2;enic filaments, sarcinas, fusiforms, and Gram- 



O JIT 



negatix'e rods, all strains indigenous to the hamster (Fitzgerald and 

 Keyes, 1960, 1963). Although cariogenic streptococci seem to have 

 a proclivity for forming plaque, it should be emphasized that not all 



