252 THE PROTOZOA 



Amoeboid movement always starts in the ectoplasm. In addition to the nucleus, 

 which the so-called chromatin-staining methods of Romanowsky bring out as reddish 

 areas, or black with iron haematoxylin, we frequently observe aggregations of chro- 

 matin-staining material in the cytoplasm. These cytoplasmic chromatin bodies 

 (chromidial bodies) are of importance in differentiating the encysted pathogenic 

 amoeba from the nonpathogenic one. This extranuclear chromatin is supposed to 

 play a part in the more intricate divisions which such protozoa undergo. Food 

 vacuoles and contractile vacuoles are present in many rhizopods. 



INTESTINAL AMCEB^E 



There are certainly two species of intestinal amoebae having man 

 for a host, the one pathogenic, Entamceba histolytica and the other a 

 harmless commensal, Entamoeba coli. 



Schaudinn, in 1903, described the pathogenic amoeba, which he named E. histolyt- 

 ica, as follows: i. Distinct, highly refractile and tenacious ectoplasm. He consid- 

 ered this tough external portion of the cytoplasm as the explanation of the ability 

 of the pathogenic amoeba to bore its way into the intestinal submucosa. 2. Eccen- 

 tric nucleus which was indistinct by reason of little chromatin. 3. Reproduction by 

 peripheral budding in which small aggregations of chromatin reached the periphery 

 of the cytoplasm and, enclosed in a resistant capsule, broke off from the parent 

 amoeba and constituted the infecting stage. 



For the nonpathogenic E. coli he noted, i. No distinction between a granular 

 endoplasm and refractile ectoplasm. 2. Centrally placed and sharply outlined 

 nucleus, rich in chromatin and 3. Encystment with the formation of eight nuclei, 

 which nuclei or amcebulae form the infecting stage. 



The pseudopodia of E. histolytica are actively projected as long finger-like processes 

 which show the ectoplasm quite distinctly, while the pseudopodia of E. coli, are 

 lobose and sluggishly projected and show a uniformly opaque grayish color. 



In 1907 Viereck and later Hartmann recognized a pathogenic 

 amoeba with four nuclei in its encysted form, to which was given the 

 name E. tetragena. 



All authorities now consider that Schaudinn made an error in observation as to 

 the existence of peripheral budding for E. histolytica, so that we recognize but two 

 types of encystment, one with a larger cyst and thicker cyst wall, with eight nuclei 

 and an absence of chromidial bodies E. coli and the other, smaller, with a thin cyst 

 wall, four nuclei and chromidial bodies in the encysted stage, the pathogenic amoeba, 

 E. histolytica. Synonym. E. tetragena. 



In the vegetative stage the human amoebae are best differentiated by the nuclear 

 structure. In E. coli the nucleus is vesicular with a thick nuclear membrane and 

 the chromatin chiefly deposited on the undersurface of the nuclear membrane. 

 In haematoxylin-stained specimens this chromatin often seems deposited in quadrant 

 aggregations. 



Whitmore noted a broad clear zone as surrounding the karyosome of the tetra- 



