ENTAMCEBA COLI 217 



with similar cytoplasm containing one, two, four, and eight nuclei in 

 which no indication of vacuole formation has been evident. He has 

 regarded these as representing the normal encystment process of E. coli 

 (Fig. 101, 1-4). 



The binucleate cysts with large vacuole appear to be derived from 

 very vacuolated and abnormal-looking precystic amoebse. It is possible 

 that the real explanation is that in some cases no vacuole is formed at 

 all, in others that one of moderate size occurs and is ultimately absorbed, 

 and that in others again there is an excessively large vacuole formed as 

 an abnormality, and that this prevents the subsequent development of 

 the nuclei. In the case of E. histolytica the cysts frequently, though not 

 invariably, contain a vacuole of moderate size which does not impede 

 nuclear division. 



It was suggested by the writer and O'Connor (1917) that there probably 

 occur races of E. coli in which the average size of the cyst differs, as in 

 E. histolytica. Matthews (1919), by measurement of a large number of 

 cysts, demonstrated that this was actually the case. 



The nuclei within the cysts have the same structure as that of the 

 adult amoeba?. According to Dobell (1919), the karyosomes are invariably 

 excentric in position, and he believes that it is usually possible to determine 

 with certainty whether the cyst is one of E. coli or E. histolytica from the 

 nuclear structure alone, provided the cysts have been properly fixed and 

 stained. In the nucleus of E. histolytica the karyosome is central. 



The arrangement of the nuclei within the cyst is subject to variations. 

 Usually, they are distributed irregularly through the cytoplasm, and careful 

 focussing at different levels is necessary in order to see and count them. 

 At other times they are grouped together, sometimes closely, at the centre 

 of the cyst, where the cytoplasm may be denser than at the periphery. 



Chromatoid bodies, first seen by Grassi (1879), and later by Casagrandi 

 and Barbagallo (1897), are occasionally seen in cysts of E. coli (Fig. 101, 8). 

 They are usually not so definitely rod-like as those in cysts of E. histolytica, 

 and may be in the form of one or more lobulated bodies or numerous, 

 small, irregularly-shaped fragments. Sometimes they are filamentous in 

 form, and the cytoplasm may be traversed by a kind of network of these 

 structures (Fig. 101, 9). The writer has seen cysts in which acicular 



1-4. Normal method of encystment, showing one to eight nuclei and absence of vacuole. 

 5. Large form with sixteen nuclei. 6. Form with two nuclei in division. 



7. Four-nucleated stage with included bacillus. 



8. Form with eight nuclei and chromatoid bodies. 



9. Form with eight nuclei and filamentous structures. 



10-12. Forms with large central glycogenic vacuole and two nuclei. 



13. Form with large central glycogenic vacuole and four nuclei. 



14. Form with two nuclei and large peripheral vacuoles. 



15. Ruptured eight-nucleated stage with hemia-like protrusion. 



