82 THE LOB OS A 



Endamoeba. 1 The species of this genus are parasitic in the 

 intestines of various animals. There is no contractile vacuole, and 

 rarely more than one short pseudopodium is protruded. Endamoeba 

 coli is commonly found in the human intestine. It is often present 

 in perfectly normal health, and is not associated with or the cause 

 of disease. The size does not exceed 50 ^. 



Endamoeba histolytica is so similar in size and form to E. coli 

 in some stages of its life-history that it has been regarded as the 

 same species, but it is now known to have a different life -history 



and to be the active cause of certain 

 "N forms of tropical dysentery. It is 

 found not only in the ulcers of the 

 intestinal mucous membrane, but 

 also in abscesses of the liver accom- 

 panying the disease. It penetrates 

 the mucous membrane of the intes- 

 tine and enters the submucosa 

 (Dopter [42]). 

 FIG. 15. The life -history of Endamoeba 



Endamoeba coli. A, a specimen with one L /o//i7.j//V/v7 Vine nrf Trof Koon f nil IT- 



nucleus in the resting condition. B,- a '^^OlytlCa Has llOt yet been lUlly 



specimen with two nuclei. (After Casa- worked OUt. It is very similar 



grandi and Barbagallo.) . . J ,-, , . 



in size and appearance to E. coh, 



but differs from it in the somewhat indefinite and variable 

 character of having usually a more distinct hyaline ectoplasm. 

 According to Lesage (43) the large cysts, similar to those of E. coli, 

 20 p in diameter, are never found in this species. In E. histolytica 

 the cysts are 3-6 //, in diameter. During the progress of the disease 

 which it causes it is constantly changing its shape and position, and 

 asexual reproduction proceeds rapidly by simple fission or multiple 

 gemmation. Cyst-formation only begins when healing commences, 

 never in the height of the disease. The encystment is preceded 

 by the rapid discharge of chromidia into the cytoplasm, and then 

 the nucleus degenerates and disappears. The chromidia then collect 

 to form a chromidial network in the ectoplasm, and subsequently 

 spherical bodies, the cysts, each surrounded by a yellowish-brown 

 membrane and containing a portion of the chromidial network, are 

 pinched off (Fig. 1 6, D). The rest of the life-history has not been 

 followed, but it has been shown that when the cysts are given to 

 cats they cause a dysenteric disease. 



Other species of Endamoeba have been described from the human 

 intestines, but it is uncertain at present whether they are or are 



1 The account given of Endamoeba coli and E. histolytica is mainly taken from 

 the important memoir of Schaiulinu. This memoir is, however, not illustrated. 

 For further information and for figures of Endamoeba coli the reader is referred 

 to the memoir by Casagrandi and Barbagallo (38), and of E. histolytica to the 

 memoir of Jiirgeus (39) and other papers mentioned in the list of literature on 

 p. 92. 



