Il8 THE AMOEBAE LIVING IN MAN 



In the karyosome of encysting amoebae a differentiation into a paler 

 cortical part and a more deeply staining central body can often be seen 

 in iron-haematoxylin specimens (cf. figs. 36, 37). This is not usually 

 visible in the mature cyst. In the latter, the nucleus has the appearance 

 of a signet-ring — especially in cysts examined in iodine (text-figs. 2A 

 to O), in which medium the peripheral granules are invisible, though the 

 karyosome and the nuclear membrane are usually to be made out with 

 ease. The granules in the nucleus of the cyst often stain very intensely, 

 so that it is necessary to stain the cysts very carefully in order to obtain 

 a correct picture of the structure of the nucleus. Sometimes one or 

 more of the granules will retain the stain more strongly than the 

 remainder, so that occasional dark granules may be seen lying among 

 the others (cf. fig. 42). 



The cysts of this amoeba are very apt to undergo shrinkage during 

 fixation, staining, and mounting ; and there is thus often a space between 

 the contents and the wall in mounted specimens. Very generally, also, 

 there is some shrinkage of the cytoplasm surrounding the nucleus, so 

 that the latter often appears — in stained preparations — to lie in a vacuole 

 (cf. figs. 38-40, 42). These appearances are, of course, artifacts ; but the 

 remarkable forms of the cysts encountered in good preparations — such 

 as figs. 41 and 42, for example — are not the result of fixation or other 

 manipulation. They are equally visible in living cysts. Fig. 38 shows a 

 badly fixed cyst of large size, in which there has been much cytoplasmic 

 shrinkage. I have drawn it because it shows a common appearance of 

 these cysts in stained preparations. It bears a striking likeness to the 

 cyst of " Entamoeba " bilischlii depicted by Prowazek and said to measure 

 i4'8/i (1912^, PI. xviii, fig. 21); and consequently, it supports my 

 identification of this form with that here described. 



Cysts of /. bi'ttschlii containing more than one nucleus are very 

 uncommon. Brug (1917) states that most unusually large cysts are 

 binucleate, but this is incorrect. I have seen several containing two 

 nuclei, but none with more. I regard them as abnormal supernucleate 

 forms, like the 8-nucleate cysts of E. nana or i6-nucleate cysts of E. coli. 

 I think Prowazek's binucleate and trinucleate " amoebae " (his figures 14 

 and 15) are really similar cysts, of irregular form, and not stages in 

 division or schizogony. It may be noted that James (1914) has inter- 

 preted Prowazek's fig. 15 as an enucleate amoeba of E. coli containing 

 three ingested yeasts — not three nuclei. This seems to me a very far- 

 fetched explanation. 



The remarkable forms so often assumed by the cysts of /. bntschlii 

 would seem to indicate that they are formed under some peculiar 

 conditions of stress or pressure. An amoeba naturally tends to assume 

 a spherical form when at rest, and about to encyst : and it has occurred 

 to me that the strange shapes of the cysts of this organism may possibly 

 be due to the fact that the amoebae are crowded together in the crypts 

 in the large intestine at the time of their encystation, so that their cysts 

 become distorted by mutual pressure. Similar strangely shaped speci- 

 mens of other protozoa, such as coccidia, which are normally oval or 

 spherical, may often be seen in cases of heavy infection where they are 

 closely packed and pressed together in the tissues. 



The mature uninucleate cysts of /. biUschlii undergo no further 



development outside the human body. They will remain unchanged — 



' xcept for the disappearance of the glycogen, as already noted — in faeces 



