74 RESEARCH IN PROTOZOOLOGY 



(7) Emhadomonas intcstinalis, probably a harmless 



commensal. 



(8) Tricercomonas intcstinalis, also probably a harmless 



commensal. 



(9) Giardia lamblia, accused of causing flagellate diar- 



rhea. 



(c) Coccidia: 



(10) Isospora hominis, the agent of a type of diarrheic 



infection known as coccidiosis. 



(d) Infusoria: 



(11) Balantidiiim coli, the ciliate responsible for balan- 



tidial dysentery. 



2. Species transmitted by the contamination of food or drink by 



trophozoites : 



(12) Trichomonas hominis, another flagellate accused of 



causing diarrhea. 



3. Species transmitted by contact in the trophozoite stage: 



(13) Endamccha gingivalis, an amoeba that lives in the 



mouth and that has been accused, probably un- 

 justly, of causing pyorrhea. 



(14) Trichomonas bticcalis, apparently a harmless flag- 



ellate living in the mouth. 



(15) Trichomonas vaginalis, a flagellate living in the 



vagina that may be pathogenic. 



TRANSMISSION BY CONTACT 



Endamccha gingivalis. The two species of protozoa that occur 

 in the human mouth are probably transmitted by contact; that 

 such a method of transmission is effective is indicated by the fact 

 that a large percentage of the general population are infected. 

 Endamocha gingivalis lives in the tartar of the teeth and in the 

 materia alba around them. The exact relation between this species 

 and the host is not known. It was once supposed to be the causa- 

 tive agent of pyorrhea, but is now usually considered harmless. 

 Kofoid (1928) has recently considered this subject in some detail. 

 The transmission of E. gingivalis appears to take place in the 

 trophozoite stage only. Cysts have been described, but there is no 

 evidence that they really exist, although Wenyon (1926) states 



