274 P- II- KKYES AND II. Y. JORDAN 



iiomenon merely accidental or coincidental? Orland (1946) noted 

 that streptococci were found in great nuni])ers in hamsters with 

 highly active caries. Although he recovered many lactobacilli, among 

 other bacterial t\pes, he mentioned that the streptococci might be 

 less aciduric than lactobacilli, and went on to speculate that the 

 source of these bacteria might be in the less acid environment of 

 deeper cavities. Harrison (1948) stated: "It is presumed that bac- 

 teria mav cause dissolution of one or more components of the en- 

 amel structure, either to secure their own metabolic requirements or 

 as an incidental or accidental consequence of the release of harmful 

 metabolic products on the enamel surface," 



In the hamster, plaques develop on coronal surfaces of the teeth 

 and in the gingival sulcus when certain dietarv substrates are avail- 

 able and specific types of bacteria are harbored in the alimentary 

 canal. As previouslv stated, neither one of these factors by itself 

 appears adequate to induce the phenomenon. 



It cannot be too strongly emphasized that none of those regions of 

 the body, to which bacteria can gain entrance by the normal portals, 

 provides a virgin soil in which any newcomer may flourish. It is just as 

 impossible to ensure the proliferation of a particular bacterial species by 

 introducing it into the mouth, as it is to ensure a crop of a particular 

 plant by scattering seeds in a field already occupied by a pre-existing 

 plant-association. The newcomer will have little chance of survival, un- 

 less it is adapted to occupy some definite place in its new environment. 

 It is fairly certain that those pathogenic bacteria which spread readily 

 from host to host owe their capacities in this direction to their ability to 

 colonize on skin or mucous surfaces, or to escape from the superficial 

 environment to the underlying tissues, (\^^ilson and Miles, 1955.) 



The findings of Fitzgerald and Keyes ( 1960 ) have indicated that 

 many types of acidogenic bacteria normally found in the mouths of 

 hamsters do not cause plaque formation even when a high-carbo- 

 hydrate low-fat diet passes through the mouth and alimentary canal; 

 i.e., the teeth generally remain remarkablv free of these bacterial 

 accumulations. When colonization of cariogenic microorganisms does 

 occur and when the tooth is in a susceptible state (newly erupted 

 and low in fluoride content), demineralization and invasion rapidly 

 occur (Keyes, 1959). The findings of Fitzgerald and Keyes (1960) 



