122 



VIII. 



GENUS DIENTAMOEBA JEPPS & DOBELL, 1918. 



There is only one species of this genus known — Dientainoeba fragilis, 

 which I have ah-eady described in detail in a joint paper (Jepps and 

 Dobell, 1918). I shall, therefore, merely summarize here as briefly as 

 possible what has there been said. 



History and Nomenclature. 



D. fragilis was probably discovered, though it was not described, by 

 Wenyon in 1909. It was later rediscovered independently by Miss M. W. 

 Jepps and by myself in 1917. We described seven cases of infection, 

 which, with VVenyon's original case, make 8 known cases in all. I have 

 found no others since, and, so far as I am aware, none have been 

 recorded.* The organism is probably rare, but not so rare as these 

 figures appear to indicate ; for it is extremely delicate, and perishes soon 

 after leaving the body. Consequently, infections must often be over- 

 looked. The nomenclature has been fully discussed in my earlier paper 

 with Miss Jepps, and need not be reconsidered here. There can be no 

 doubt that this organism is generically distinct from all other amoebae 

 of the human gut. 



Description. 



D. fragilis is a very small amoeba. When rounded it measures from 

 3"5 yu, to 12 /i in diameter, its usual size being about 8-9 fi. It is 

 thus similar in size to E. nana and the smallest precystic forms of 

 E. histolytica. 



The living amoebae are actively motile. They show a well-marked 

 differentiation between their ectoplasm and endoplasm. The pseudo- 

 podia are typically composed almost entirely of ectoplasm, and are few, 

 flattened, leaf-like, and often lobed or indented. The endoplasm is 

 granular, and usually contains numerous food- vacuoles ; but a con- 

 tractile vacuole, as in other parasitic amoebae, is absent. During locomo- 

 tion the animal has a somewhat snail-like appearance — the hyaline pseudo- 

 podia being in advance, the granular endoplasm concentrated in a fairly 

 definite rounded mass posteriorly. Like other intestinal amoebae, the 

 organism is colourless. 



The most characteristic feature of D. fragilis is its nuclear system. 



* Since the publication of the description of this organism five cases of infection have 

 been reported to me privately by others. On investigation none of these proved to be 

 infections with Dzefitatnoeba in reality. I record them to show the errors which can occur 

 in diagnosis. Two of them were small free-living "//;««x" amoebae, in stale stools. 

 Two others were leucocytes, in stools containing pus ; and the remaining one was an 

 infection with E. nana, in which many of the amoebae were parasitized by Sphaerita — 

 the spore-morulae of which were mistaken for nuclei. 



