AMCEB.E 



221 



was bacteriologically sterile. Shiga in 1898 separated the bacillary type of dysen- 

 tery from the amoebic one. Schaudinn, in 1903, stated that E. histolytica was the 

 pathogenic amoeba of man. Viereck found encysted amoebae in dysenteric stools 

 containing four nuclei. This amoeba is now believed to be the common pathogenic 

 amoeba of man and is named E. tetragena. 



Entamceba tetragena. This amoeba has a homogenous and highly 

 refractile ectoplasm with a nucleus richer in chromatin than E. his- 

 tolytica. It has a central karyosome which varies in size. 



FIG. 59. Human amoebae showing vegetative and encysted stages. Water 

 amoebae for comparison. (ia) Entamceba coli; (16) E. coli (encysted); (2) E. 

 japonica; (30) E. histolytica; (36) E. histolytica (encysted); (30) E. histolytica per- 

 ipheral buds; (40) E. tetragena; (46) E. tetragena (encysted); (50) water amoeba, 

 vegetative; (56) water amoeba, encysted. 



In an iron haematoxylin preparation this karyosome shows a central spot or 

 centriole which niay fill up most ol the nuclear space but in such case is surrounded 

 by a clear zone with the karyosome ring outside. Hartmann found that some of 

 Schaudinn's specimens were E. tetragena and the belief is now growing that the life 

 history of a nucleus resolving into chromidia which collected at the periphery and 

 formed the peripheral infecting spores was an error in observation on the part of 

 Schaudinn and that the true life history of the pathogenic human amoeba is that of 

 E. tetragena. In such case E. tetragena and E. histolytica applying to the same 



