VIII, B, 4 Walker and Sellards: Entamcebic Dysentery 289 



dinn and that the life cycle of Entamoeba histolytica includes 

 the development of "tetragena" cysts. 



Wenyon (1912), Darling (1912), and Hartmann (1912) have 

 subsequently come to the same conclusion, although Darling 

 and Hartmann persist in calling the species "Entamceba tetra- 

 gena." However, on the basis of priority. Entamoeba histolytica 

 Schaudinn must remain the valid name of this species. Craig 

 (1913) still maintains that Entamceba histolytica and "Enta- 

 mceba tetragena" are distinct species." 



The view that we are here dealing with but one species has 

 received further support from observation of the morphological 

 changes that take place in Entamoeba histolytica during the 

 course of the disease in experimentally infected men. There 

 has been found to exist a more or less definite series of mor- 

 phological changes in the entamoebse that are found in the stools 

 which appear to be correlated with the clinical symptoms in 

 the host. Men fed Entamoeba histolytica show "tetragena" cysts 

 in their stools, after a short incubation period, and these cysts 

 persist so long as the stools of the parasitized individual remain 

 formed. When the stools become soft or diarrhoeal, the "tetra- 

 gena" cysts are replaced by postencysted or preencysted enta- 

 moeba which are small and inactive and have a nucleus more 

 or less rich in chromatin. These forms correspond to Elmas- 

 sian's "Entamoeba minuta." If chronic dysentery with faecal 

 stools mixed with mucus and blood develops, larger and more 

 active forms appear which still contain nuclei rich in chromatin 

 and many of which show the karyosome structure characteristic 

 of "Entamoeba tetragena." ■ In acute attacks of dysentery, in 

 which mucus and blood practically free from faeces are passed, 

 these forms are largely replaced by entamoebse having an indis- 

 tinct nucleus that contains a minimum amount of chromatin, 

 which is characteristic of Entamoeba histolytica Schaudinn. In 

 untreated cases that recover spontaneously from the attack of 

 dysentery, this series of morphological changes is repeated in 

 the inverse order, ending with the reappearance of "tetragena" 

 cysts in the formed stools of the convalescent individual. These 

 changes in the morphology of Entamceba histolytica, which are 

 connected with the developmental cycle of the organism, probably 



"Since this paper was written, Craig (1913'i and IQIS^) has changed 

 his opinion and now agrees that Entamceba tetragena Viereck is identical 

 with Entamoeba histolytica Schaudinn. He gives me full credit for being 

 the first definitely to state the identity of these two species. 



