356 



PROTOZOOLOGY 



that there are several varieties or races of this amoeba, as has 

 already been mentioned (p. 179). 



Entamoeba histolytica, commonly known as "the dysentery 

 amoeba," was first definitely recognized by Losch in Russia in 1875. 

 It is now known to be widely distributed in tropical, subtropical 

 and temperate regions alike, although it is more prevalent in warmer 

 regions. The incidence of infection depends mainly on the sanitary 





Fig. 168. Diagram showing excystment and a common way by which 

 a metacystic amoeba of Entamoeba histolytica divides into 8 uninucleate 

 amoebulae (Dobell). 



conditions of the community, since the organism is voided from host 

 in faeces. Faecal examinations which have been carried on by nu- 

 merous investigators in different countries of the world, reveal that 

 the incidence of infection is as high as over 50 per cent in some areas. 

 According to Craig (1934), 49,336 examinations made by many 

 observers in various parts of the United States show that the infec- 



