HOST-PARASITE RELATIONS! INTESTINAL PROTOZOA 



yon (1926) states that they ''probably occur." If they 

 do, they must play a minor role in the life-cycle of the 

 organism. Transmission from host to host no doubt takes 

 place in the trophozoite stage and plenty of opportunity 

 is afforded for direct passage during kissing. It is thus 

 easy to account for the high incidence of infection in the 

 general population which probably averages at least 50 

 per cent. This species of amoeba, although in the active 

 stage when disseminated, is probably passively carried 

 from mouth to mouth. The absence of a cyst stage in 

 the only amoeba of man that is transmitted by direct 

 contact is worthy of note. 



Pathogenicity. E. gingivalis lives in various places in 

 the mouth, but especially in the tartar of the teeth and 

 in the materia alba around them; it has been reported 

 from many suppurative and inflamed conditions of the 

 mouth and throat. That this species does not require 

 access to the tissues is indicated by the fact that Lynch 

 (1915c) found them in the crevices between the false 

 teeth of persons with healthy gums. Various new species 

 have been described from abscesses in the jaw, tonsils, 

 etc., but these were probably all somewhat modified E. 

 gingivalis. The presence of large numbers of these 

 amoebae in the lesions of pyorrhea alveolaris led Smith 

 and Barrett (191 5) and Bass and Johns (191 5) to con- 

 clude that they are responsible for this disease, and on 

 their recommendation emetin was widely used in its 

 treatment. More recent studies indicate that the species 

 is harmless. Its food consists principally of leucocytes 

 and a few bacteria (Kofoid and Swezy, 1924c). Smith 

 and Barrett (191 5) record the ingestion of red cells and 



126 



