PART II. CHARACTERS AND DIAGNOSIS 91 



of E. nana were seen by one of us in cases in London during the 

 latter part of 1915, but they were thought to be of a vegetable 

 nature, or possibly a stage in the encystment of tetramitus. One 

 of the four-nuclear cysts was figured in a paper on the " Human 

 Intestinal Protozoa" (Lancet, November 27, 1915, and Journal of 

 the Royal Army Medical Corps, December, 1915, fig. 17) as 

 a possible later stage of development of the cyst of tetramitus, 

 which was also present. The small free amoebae were also met with 

 on several occasions but were regarded as Amoeba Umax, though a 

 failure to obtain a culture on agar media on which A. Umax was 

 growing threw some doubt on this. In Egypt, however, we have 

 had ample opportunity of studying this amoeba in cases which have 

 been under daily observation in hospital and we have been able to 

 definitely associate the small oval or spherical cysts with the small 

 amoeba. The type of infection with E. nana resembles that of 

 other intestinal protozoa. The amoebae or their cysts may be 

 passed continuously over comparatively long periods, or the infec- 

 tion may be apparent for only a few days and then vanish only to 

 reappear again after an interval. E. nana occurred in a good 

 number of the cases which were being controlled in hospital for 

 E. histolytica infections (see Tables of Cases, pages 100-177, etc.). 



Very striking are the cases where cysts only in large numbers 

 are passed daily in a constipated stool. The administration of a 

 saline purge to such cases produces enormous numbers of minute 

 amoebae. In the soft unformed stool it is usual to find the free 

 amoebae and the cysts associated. 



One must be careful to distinguish the cysts of E. nana from 

 the cysts of the smaller strains of E. histolytica. The resemblance 

 may be very striking and at times it may be necessary to stain 

 films in order to arrive at a diagnosis. The small E. histolytica 

 cysts are generally spherical or nearly so, while the cysts of E. nana 

 are typically oval, very much like small lamblia cysts, though in- 

 ternally no structure can be detected. Spherical and irregularly 

 shaped cysts of E. nana also occur, but these are always associated 

 with the more typical oval forms. The cysts are never bottle- 

 shaped like the cysts of tetramitus, with which confusion might 

 take place. 



Free Amoeba. The free-living amoebae are very small and have 

 a diameter of 5 to 10 microns. Their structure varies considerably. 

 They may be very vacuolated and contain bacteria and cocci or they 

 may appear quite homogeneous (Plate I, figs. 10 and 11).* The 



* See inset between pages 148 and 149. 



