RHIZOPODA 403 



the diameter measuring 10 to 70/1. The protoplasm is slightly 

 granular and shows distinctly an alveolar structure. The d!s-~ 

 tinction between ectoplasm and endoplasm is apparent only in 

 the pseudopodia. There is no contractile vacuole. Food sub- 

 stance is present in the cytoplasm, bits of vegetable material, 

 bacteria and, rarely, red blood cells. The nucleus is round, ve- 

 sicular and enclosed in a nuclear membrane. In its center is a 

 relatively large mass of chromatin and there are numerous smaller 

 masses of chromatin at the periphery beneath the nuclear mem- 

 brane. Multiplication in the vegetative stage takes place by 

 binary division as a rule, but multiple division preceded by re- 

 peated division of the nucleus also occurs. 



E. coli discharges all food material from its cytoplasm before 

 encystment so that the cell is clear and the nucleus plainly visible. 

 A large vacuole in the cytoplasm usually makes its appearance 

 and is present during the first and second division of the nucleus 

 in the cyst. It is large in those cysts in which much chromatin 

 escapes from the nuclei into the cytoplasm as chromidia, and it 

 usually disappears when the four nuclei have been formed. A 

 further division of the nuclei gives rise to eight and this is the 

 usual number present in the fully developed cyst of E. coli, al- 

 though rarely ten or even sixteen nuclei may be observed. 1 The 

 self-fertilization, autogamy, described by Schaudinn as occurring 

 early in encystment has not been observed by Hartmann, and 

 its actual occurrence seems questionable. The developed cyst 

 with eight nuclei is about i5/z in diameter and is considered to be 

 definitely characteristic of this species. 



E. coli is generally regarded as a harmless commensal in the 

 human intestine. It is however impossible to exclude the possi- 

 bility that it may contribute to the aggravation of pathological 

 conditions present in the digestive tract. (Compare with Bacillus 

 coli.) Its common occurrence in healthy men speaks against 

 its possessing any very specific and powerful pathogenic property. 



1 Hartmann and Whitmore: Archiv f. Protistenkunde, 1912, Bd. XXIV, S. 

 182-194. 



