TRANSMISSION OF INTESTINAL PROTOZOA 75 



that they "probably occur." If they do they must play a minor 

 role in the Hfe-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 gen- 

 eral population which probably averages at least fifty per cent. 

 This species of amoeba, although in the active stage when dissemi- 

 mated, is probably passively carried from mouth to mouth. The 

 absence of a cyst stage in the only amoeba of man that is trans- 

 mitted by direct contact is worthy of note. 



Endamoebse have been reported from the mouths of certain 

 lower animals, including the cat, dog and horse. Attempts have 

 been made to transmit amoebae from the mouth of man to certain 

 lower animals. Hecker (1916) was unable to infect guinea-pigs 

 and Drbohlav (1925) did not succeed in obtaining infection in a 

 young dog in the gingivae of which Endamoeha gingivalis grown in 

 culture was inoculated. Hinshaw (1928), however, was successful. 

 It has been suggested that the amoeba of the mouth of man 

 is the same species as E. histolytica of the intestine. The stud- 

 ies of Kofoid and Swezy (1924), however, indicate that this 

 is highly improbable. If they should prove to be the same 

 species transmission would probably be due to the ingestion 

 of food or drink contaminated with material containing E. his- 

 tolytica. 



Trichomonas huccalis. This mouth-inhabiting flagellate is wide- 

 spread, occurring in perhaps a third or more of the general popula- 

 tion. As in the case of E. gingivalis and E. histolytica, it has been 

 suggested that T. huccalis of the human mouth and T. hominis of 

 the human intestine belong to the same species, the latter being 

 specimens from the mouth swallowed by the host. Most of our 

 evidence, however, indicates that these two flagellates belong to 

 different species. Both Hogue (1926) and Hinshaw (1926) found 

 that T. huccalis is more frequently present in the mouths of per- 

 sons suffering from pyorrhea, acute gingivitis or abscessed teeth 

 than in persons with normal mouths. Hogue also found that strains 

 of T. huccalis grown in culture tubes differed with respect to their 

 resistance to temperature and to the pH of the medium. It thus 

 seems probable that the effectiveness of the transmission, which no 

 doubt usually results from the passive transfer of the organisms 

 from one host to another during kissing, depends somewhat on the 



