240 FAMILY: AMCEBIDyE 



sequently corrected by the writer and O'Connor (1917). The cyst, which 

 has four nuclei in the mature condition, is typically ovoid in shape, and 

 measures from 8 to 10 microns in length and about half this in breadth 

 (Fig. Ill, 5-12). As a rule, one side is less convex than the other, so 

 that the outline is not quite symmetrical. Sometimes the cysts are 

 spherical, and between these and the typically ovoid forms various 

 gradations occur. The nuclei in the cysts are constituted similarly to 

 those of the amoebse, but in the four-nuclear cysts they are very minute. 

 A characteristic picture is that of a large chromatin body on one side 

 of the nucleus connected to a smaller body at the other side, as sometimes 

 occurs in the free forms. 



Attention has been drawn by Dobell (1919) to the occasional presence 

 in the cytoplasm of a glycogen vacuole (Plate II., 22, p. 250). In some 

 batches of these amoebse a large proportion of the uninucleate cysts 

 possess such a vacuole, while in others it is not so apparent. As noted 

 by Swellengrebel and Winoto (1917), the glycogen gradually disappears 

 in cysts kept for some days outside the body. Dobell has noted the 

 occasional presence of eight instead of the usual four nuclei within the 

 cyst. The writer has also seen these form •. The cysts may contain certain 

 filamentous bodies the nature of which is not clear. Dobell suggests they 

 may be parasitic or symbiotic bacteria, or possibly chromatoid bodies. 



In fresh saline preparations the cysts appear as perfectly clear homo- 

 geneous structures. The nuclei can rarely be detected, and even in 

 iodine solution they are often difficult to see (Plate II., 17-22, p. 250). 

 In specimens stained with iron haematoxylin they are generally quite 

 evident, but it is difficult to gauge the exact degree of differentiation on 

 account of the small size of the cysts. The nuclei may occupy any position 

 in the cyst, but not infrequently they are grouped at one end. 



E. nana is an inhabitant of the large intestine, and the writer (1920), 

 in sections of the large intestine, has noted the presence of these amoebae 

 in the lumen of the glands. There was no evidence that they could invade 

 the tissues. Whether the amoebae can also live in the small intestine, as 

 Dobell (1919) conjectures, is not known. There is no indication that E. nana 

 is in any way pathogenic, and in this respect it resembles the harmless E. coli. 



Attempts at cultivation of E. nana on solid medir. have not met with 

 success. If faeces containing them are smeared on the surface of suitable 

 agar medium, cultures of small amoebae of the same size may be obtained, 

 but these are merely developed from cysts of free-living forms. 



Several observers have undoubtedly seen E. nana in human faeces, 

 gllld have thought they have obtained cultures of it in agar plates. It 

 is probable that as the E. nana perished the cysts of free-living amoebae 

 gave rise to a culture, and produced an erroneous impression of culture 



