ENDOLIMAX NANA IO7 



variable number of very small refractile granules. These are more 

 clearly seen in the living cyst than in stained specimens. They give 

 some of the metachromatic staining reactions of volutin, and are 

 probably composed of this substance. They probably do not consist 

 of chromatin, and are therefore not comparable with the chromatoid 

 bodies in the cysts of Entanioebae and many free-living species. In 

 uninucleate cysts the nucleus is usually relatively large (up to about 3/i), 

 and its karyosome relatively small, often having the form of a larger 

 eccentric mass of chromatin united by a fine thread with a much 

 smaller granule (cf. fig, 25, PI. II) — a type of nucleus specially noted by 

 Wenyon and O'Connor (1917). The nucleus later divides into two (fig. 

 26), and each of these again divides into two (fig. 27). Except for their 

 progressive reduction in size, the resting nuclei in the uninucleate, 

 binucleate, and quadrinucleate cysts show no change of structure. The 

 arrangement of the chromatin in them is very hard to study accurately, 

 on account of their very small size, but they show no conspicuous 

 differences from the nuclear types observable in the active organisms. 



Mature living cysts of E. nana are typically oval, and measure 8-10 /i 

 in length and 7-8 /x in width. In fixed and stained specimens they appear 

 slightly smaller. The nuclei in the mature cysts (stained) have a diameter 

 of about I ixio i"3 /a. (Cf. fig. 8, PL I, and figs. 27-29, PI. II.) Except 

 for the volutin granules already noted, the mature cysts typically con- 

 tain no visible contents besides their four characteristic nuclei. The 

 latter often lie near together towards one end of the cyst, but they may 

 occupy any positions in relation to one another. In iodine solution the 

 cysts stain a uniform yellow colour, and their nuclei are, as a rule, 

 inconspicuous ; though their karyosomes can generally be made out, 

 with a little care, in this medium, and sometimes their nuclear membranes 

 as well. 



If a stool containing a large number of encysting amoebaeand newly- 

 formed cysts is examined in iodine solution, it will generally be found that 

 many of the former show diffusely stained brown patches in their 

 cytoplasm : and among the encysted forms there is usually but little 

 difficulty in finding some which show definite contained masses giving a 

 typical glycogen reaction. These glycogen masses are usually particularly 

 prominent in binucleate cysts — as in E. coli ; but they are also found 

 sometimes in quadrinucleate and uninucleate cysts. They give other 

 characteristic reactions of this substance, and show typical staining with 

 Best's specific carmine method (see fig. 9, PI. I). Glycogen cannot always 

 be demonstrated in the cysts of E. nana, and it is usually commoner in 

 the cysts contained in soft and diarrhoeic stools — in which free and 

 encysting forms and young cysts are numerous — than in those found in 

 formed and solid stools — which contain a large proportion of mature 

 cysts and no free amoebae. Mature cysts of E. nana remain unchanged 

 in human faeces for several weeks, if they are not desiccated. But the 

 glycogen, if present originally in them, disappears completely — as noted 

 already by Swellengrebel and Mangkoe Winoto (1917). 



Several variations in the cysts of E. nana require further notice. 

 Their form may range from the typical oval to that of a sphere. Very 

 rarely they areof irregular shape, showing slight constrictions or bulgings 

 which give rise to a variety of different forms. Their size, too, varies. 

 Very small cysts, down to 6 /^ in mean diameter, and very large ones, up 

 ■ II /i or slightly more, may occasionally be met with (cf. figs. 30 and 



