114 THE AMOEBAE LIVING IN MAN 



granule can be seen in the centre — as figured by Prowazek (1912^, 

 figs. 13, 16) — but there seems no justification for calHng this a centriole. 

 I have discussed similar appearances in other amoebae elsewhere (1914), 

 and shall not discuss the interpretation of them further here. 



The nuclear membrane is fairly well developed, and stains readily. 

 Occasionally it shows very fine granules (? chromatin) imbedded in it, 

 but these cannot usually be seen clearly. Between the karyosome and 

 the membrane there is the usual " clear zone," which is occupied in the 

 present species by a layer of fairly large granules — so-called " peripheral 

 chromatin." These granules usually lie in a single layer. They stain 

 somewhat deeply with iron-haematoxylin, but on extraction give up the 

 stain more readily than the karyosome. They can thus be completely 

 decolorized, and counterstained with eosin or other plasma stains, 

 whilst the karyosome remains deeply coloured (cf. fig. 32), In ordinary 

 iron-haematoxylin preparations they are often overstained, so that they are 

 confounded with the karyosome ; or they may be completely decolorized, 

 so that they disappear. Very often, in such preparations, only their 

 outlines are visible ; and this gives rise to an optical effect suggesting the 

 presence of a network or series of septa connecting the karyosome with 

 the nuclear membrane. This is the structure described in the nucleus 

 of " E." biitschlii by Prowazek. By using suitable counterstains and good 

 lenses with proper illumination it is not difficult to convince oneself that 

 his interpretation was incorrect, and that the clear zone is really occu- 

 pied by a layer of small granules and not by a network. (Cf. figs. 10, 

 32, 34.) I note that Kuenen and Swellengrebel (1917) have already 

 observed the presence of "peripheral chromatin" in the nucleus of this 

 form. It may be noted further that these granules are generally disposed 

 in a single layer in the active amoeba; and that they are often distinctly 

 separated from the nuclear membrane but apparently imbedded in the 

 karyosome, whose outline often appears slightly stellate in consequence 



(fig. 32). 



I lay some stress on these nuclear characters, as they supply the only 

 means of distinguishing the amoebae of this species with certainty.* All 

 active amoebae, of whatever size, appear to possess the same nuclear struc- 

 ture. In very small forms, however, it is impossible to make out all the 

 details with precision. Such organisms (fig. 33), and also many degenerate 

 or badly fixed and stained individuals, cannot always be distinguished 

 with certainty from similar small or degenerate specimens of E. nana. It 

 may also be very difficult, or impossible, to distinguish very small speci- 

 mens of /. biitschlii from small uninucleate individuals of Dientanioeba 

 fragilis. 



I. biitschlii appears to feed chiefly upon small micro-organisms in the 

 intestinal contents. To judge from the inclusions in its food-vacuoles, 

 its food habits are closely similar to those of E. nana. 



The habitat of the organism has not been determined with certainty : 

 but from the close parallel between the appearance of the free and 

 encysted forms and those of E. coli, in the stools of persons infected 

 with both species, I judge it to be probably — like the latter — an 



* That is to say, of distinguishing them from other amoebae found in the same 

 situation. Many of the small free-living amoebae possess, of course, a nuclear structure 

 which is very closely similar. 



