70 HUMAN INTESTINAL PROTOZOA IN THE NEAR EAST 



Another feature of the cysts of E. coli which demands atten- 

 tion is the possible presence of chromidial bodies. These may be 

 single bars, very like the rods in E. histolytica cysts, or they may 

 be multiple when they take on various shapes, being either rod-like, 

 round, oval, or spindle-shaped masses, or more irregular in form. 

 Sometimes in E. coli cysts there occur numerous fine filamentous 

 structures which may show a thickening in the centre, so that they 

 are fusiform in shape. These may be arranged irregularly through 

 the cytoplasm with the eight nuclei distributed amongst them, or 

 the eight nuclei may be grouped together in a central mass of 

 cytoplasm, while the fusiform bodies are arranged tangentially 

 around this central mass. The fusiform structures may be few in 

 number, or very numerous. We have some evidence that they 

 are really bacteria which have not been extruded by the encysting 

 amoebae. The possibility of their being parasites of the amoeba 

 has also to be considered. 



It has been pointed out before that the type of E. coli cyst 

 most commonly met with in the stools is the eight-nuclear cyst, 

 while the stage with two or four nuclei is more rarely seen. An 

 exception to this rule, however, is the frequent occurrence of the 

 type of cyst with large central vacuole and only two nuclei. 

 Sometimes nearly every cyst in a stool is of this type. These 

 bi-nuclear, vacuolated cysts are generally quite green in colour, 

 and more refractile than the clear transparent non-vacuolated eight- 

 nuclear cysts. It seems to us that there is something abnormal 

 about these cysts, and it still remains to be proved that they are 

 capable of further development. We cannot agree with Kuenen 

 and Swellengrebel that these two-nuclear vacuolated cysts are an 

 essential stage in the development towards the unvacuolated eight- 

 nuclear cysts. As a matter of fact, the one, two, and four-nuclear 

 cysts without the central vacuole are far from uncommon when one 

 happens to get a stool containing the actually encysting amoebae. 

 The two-nuclear cysts with central vacuole seem to be derived from 

 certain green highly refractile amoebae which have a much vacuo- 

 lated cytoplasm. They are fairly common, and are often seen as 

 green discs of cytoplasm, the central part of which is either a 

 single large vacuole or several smaller ones. The nucleus in these 

 amoebae may or may not be clearly visible. 



Suggestions have recently been made that the distinction 

 between the cysts of E. coli and E. histolytica are not so definite 

 and marked as some maintain. It has been even hinted that the 

 one may be only a smaller variety of the other. Gauducheau has 



