ROBERT HEGNER 671 



whereas only non-infective trophozoites are passed during an acute period of the 

 disease. 



Cysts can reach the intestine of man only by way of the mouth and hence efforts 

 to protect food and drink from fecal contamination furnish the best means of preven- 

 tion. In countries where night-soil is used as fertilizer, for example, in China, uncooked 

 vegetables and fruit should be eaten only after being thoroughly washed, and im- 

 mersed for ten seconds in boiling water. Infection apparently spreads throughout a 

 family if one member becomes a host, hence particular attention should be directed 

 toward sanitary conditions in the home. 



Improvements in water supplies and general sanitation are recommended for the 

 protection of communities, since there is good evidence that infective cysts are carried 

 in water supplies and that flies may transport cysts from infected fecal material to 

 food and drink. The determination and treatment of carriers in the general popula- 

 tion has been suggested as a means of preventing the spread of amebiasis, but the 

 cost of such a campaign is at the present time prohibitive. Cresol appears to be the 

 best disinfecting agent for destroying cysts in fecal material. 



ENDAMOEBA COLI 



This species resembles Endamoeha histolytica in its life-cycle and is no doubt trans- 

 mitted in the same manner. That it is very successful in gaining access to and estab- 

 lishing infections in man is evident from the fact that about 50 per cent of the general 

 population appears to be infected with this organism. 



Endamoeha coli lives in the large intestine where it feeds on bacteria, yeast, starch 

 grains, and all sorts of debris. Cases have been reported of amebae of this type that 

 ingested red blood cells, and there is certain evidence that E. coli, under extraordinary 

 conditions, may invade the intestinal wall, but from the data available it is safe to 

 state that only rarely if ever does this species produce intestinal lesions. 



OTHER INTESTINAL AMEBAE 



Endolimax nana. — This is a harmless species that lives in the large intestine of 

 about 25 per cent of the general population. Its life-cycle is similar to that of End- 

 amoeba coli, and there is no evidence that lesions of any kind are produced by it in 

 man. 



lodamoeha williamsi. — This is another inhabitant of the large intestine; it occurs 

 in about 10 per cent of the general population. It is apparently a harmless commensal. 



Dientamoeba Jragilis. — This species is also an inhabitant of the large intestine 

 but is exceedingly rare and hence no discussion of its host-parasite relations is 

 possible. 



Endamoeba gingivalis. — E. gingivalis differs from other endamebae in the absence 

 of a cyst stage in its life-cycle. This is probably correlated with the fact that trans- 

 mission no doubt takes place by direct contact during kissing, since this organism 

 lives in the human mouth. The incidence of infection is not definitely known, but 

 probably 50 per cent of the general population harbor this species. The tartar of the 

 teeth and materia alba around them and decayed spots are the particular habitats 

 of this species. At one time it was supposed that E, gingivalis was responsible for 



