88 AMOEBAE LIVING IN MAN 



The glycogen in the cysts of £. coli appears to have been first noted 

 by McCarrison (1909) ; though he did not recognize it as such and 

 merely recorded the presence of a "port-wine staining area" in the 

 2-nucleate and 4-nucleate, but not in the 8-nucleate, cysts of his 

 " Amoeba I," when they were examined in iodine. His figures and 

 account leave no doubt that he was dealing with the cysts of E. coli. 

 Kuenen and Swellengrebel (1913, 1914) investigated the contents of the 

 cysts more carefully, and showed for the first time that the iodine-staining 

 substance is glycogen. Their observations have been repeatedly confirmed 

 since. In my opinion the glycogen in the cysts of Entainoebae is a most 

 important and useful diagnostic character (cf. Dobell and Jepps, 1917). 



Several authors — including Wenyon and O'Connor (1917) and Mathis 

 and Mercier (igiyd) — regard the cysts of E. coli which contain glycogen 

 as abnormal forms, incapable of further development. This view seems 

 to have originated with Schaudinn (1903), but I think it is a mistake, and 

 one due largely to the fact that too much importance has been attached 

 to the appearances of the glycogen-containing cysts in stained prepara- 

 tions. In these, the area originally occupied by the glycogen appears as 

 a clear space (cf. figs. 57-60, PI. IV), or vacuole : and such "vacuolate" 

 cysts may well appear to be degenerate if the fact that they once con- 

 tained glycogen is overlooked. These workers, at all events, never even 

 mention that the " vacuole " really contains glycogen — though this can 

 be readily demonstrated. The "vacuole" is not an empty space, nor 

 the result of degeneration. And when it is remembered that the majority 

 of binucleate cysts of E. coli contain this glycogen "vacuole," and 

 that similar glycogen inclusions occur in the cysts of most other para- 

 sitic amoebae at some stage in their development, it is difficult to believe 

 that it is an abnormality. It is difficult to believe that most individuals of 

 E. coli should store up glycogen — for no purpose — and then die without 

 completing their development. That cysts containing a large glycogen 

 " vacuole" are, moreover, capable of further development has been 

 shown by Wenyon himself (1907) in the case of E. muris." 



Chromatoid Bodies. — As already noted, chromatoid bodies are not 

 always present in the cysts of E. coli. They are often in the form of 

 small granular or rod-like bodies in the earliest stages of development 

 (fig. 56, PI. IV), and are frequently larger and more abundant in 

 binucleate cysts (fig. 60). In mature 8-nucleate cysts they are as a rule 

 apparently absent : but well-stained preparations of freshly-passed cysts, 

 if examined with care, generally show one or more very small chromatoid 

 bodies lying among the nuclei (cf. figs. 14 (PI. I), and 62 (PI. IV)). 

 Sometimes, however, the cysts of E. coli contain, at all stages of develop- 

 ment, chromatoid bodies which are quite as abundant as those usually 

 seen in the cysts of E. histolytica. They differ, as a rule, in form ; being 

 typically acicular or filamentar, and often aggregated into sheaves (figs. 

 63 — 66, PI. IV). In general, they may be compared with fragments of 

 splintered glass. 



Sometimes the cysts of E. coli contain chromatoid bodies of a remark- 

 able filamentar type (fig. 65, PI. IV). The filaments are long and slender, 

 and wound in a sort of skein inside the cyst, around and among the 



• He has observed and figured the "vacuole" at all stages in development of a 

 living cyst of this species, though without noting the presence of glycogen in it. 



