THE BACTERIA OF THE HUMAN BODY 323 



posed of stratified squamous epithelial cells and is constantly 

 kept moist by the saliva. The saliva contains an amylolytic 

 ferment called ptyalin. This ferment converts starch into 

 sugar. The conversion of the starch materials into sugar by 

 the ptyalin is undoubtedly favorable to bacterial action. 

 Furthermore, the stratified squamous epithelium lining the 

 mouth is continually being thrown off, and this material fur- 

 nishes excellent nitrogenous food for the bacteria which may 

 be present. 



The teeth are, of course, bathed in saliva all the time. 

 There are always present in the mouth numerous irregular 

 depressions of the mucous membrane, and these together with 

 the spaces between the teeth serve as lodging places for 

 particles of food which are kept moist by the saliva. The 

 saliva is said by some writers to be slightly antiseptic, but this 

 action is of no practical consequence. The temperature of the 

 mouth is relatively high (98.6 F. or 37 C.), and it is at once 

 evident that a better place for the incubation and growth 

 of bacteria cannot be found. The main prerequisites for 

 bacterial growth are at hand, namely, moisture, heat, and 

 organic food. 



The average mouth contains a great variety of species of 

 bacteria. Certain of the saprogenic or putrefactive bacteria, 

 the chromogenic or pigmented bacteria, the aerogenic or gas- 

 producing bacteria, and the pathogenic or disease-producing 

 bacteria may be present. One writer describing the bacteria 

 of the mouth says that almost every organism which has been 



