PAHT II. CHARACTERS AND DIAGNOSIS 93 



side of the membrane. The occurrence of this type of nucleus 

 both in the free amoebae and the cysts dispels all doubt as to the 

 identity of the two. 



As already stated, the E. nan a is of very frequent occurrence, 

 and has been constantly encountered in the course of routine 

 examination now that we have learned to identify it. The amoeba 

 has undoubtedly been seen before, but has been confused with 

 small forms of E. coli or E. histolytica, with which it is often found. 

 It has only been by careful study of a number of cases, and above 

 all of cases from which the other entamcebae were absent, that we 

 were able to exclude any connection with them. The course of the 

 infection was very strikingly followed in two cases which had been 

 cured of E. histolytica infections. The greatest amount of con- 

 fusion has probably existed between this amoeba and Amoeba Umax, 

 or the amoeba which is generally known by this name. A. Umax 

 can be cultivated from the human stool, but all our attempts to 

 obtain culture of E. nana have failed. One stool which was much 

 delayed in reaching us contained numerous minute amoebae and 

 small spherical cysts like the cysts of the amoebae which readily 

 grow on agar and which are quite unlike the cysts of E. nana. 

 This material planted on agar plates gave rise to a good culture of 

 amoebae, and the spherical cysts were there reproduced. Material 

 containing E. nana was inoculated on the same medium on the 

 same day from two cases, but no growth was obtained. It seems 

 clear, therefore, that E. nana, like E. coli and E. histolytica, will 

 not grow on agar, which is suitable for the growth of A. Umax 

 or similar forms. The amoeba which we have designated E. nana 

 corresponds with none of the amoeboid organisms which have been 

 described from the human intestine. The E. butschlii of Prowazek, 

 a much larger form, resembles it most. This author's description, 

 however, is too meagre to allow of any comparison being made. 

 Moreover, he does not describe any encysted forms. 



As regards the nomenclature of this amoeba we have placed it 

 with the entamcebae because it appears to be truly parasitic. In 

 nuclear structure, however, there are certain differences, though, 

 as with the entamcebae, the chromatin material is mostly arranged 

 on the nuclear membrane. Aggregations of chromatin are not 

 uncommon in the nuclei of E. histolytica. Furthermore, it is very 

 doubtful if nuclear structure alone can be regarded as a distinguish- 

 ing feature of the genus Entamceba. It seems safer, therefore, to 

 include this form with the truly parasitic amoeba under the name 

 Entamceba nana than to class it with the free-living non-parasitic 

 amoeba. 



