394 



BIOLOGY OF THE PROTOZOA 



amazing numbers, but to bring about encystation and excystation 

 at will while, at any stage, dysentery in kittens could be produced. 

 The tissue-invading forms of E. dysenteriae are usually from 20 n to 

 30 n in size but variations above and below these limits may occur. 

 The organism quickly degenerates outside the body and becomes 

 quiet with a thick hyaline ectoplasm, but under normal conditions 

 it shows great activity, moving occasionally like a Umax type of 

 ameba or more frequently by the formation of large blunt pseudo- 





Am 



B 



ij 



V 



/ 



cr-' 



/ 



Fig. 171. — Endamotha dysenteriae. A, typical trophic ameba with red blood 

 corpuscle found in dysenteric stools; B and C, encysted individuals about ready for 

 excystment; D, cyst with eight nuclei and chromatoid bodies. (After Cleveland 

 and Sanders, Arch. f. Protistenkunde; courtesy of G. Fischer.) 



podia which are suddenly formed and withdrawn with equal speed. 

 The endoplasm is densely granular and in addition to the nucleus 

 contains food vacuoles, "chromatoid" bodies and numerous small 

 granules which stain intra vitam with neutral red (Dobell). 



The nucleus is difficult to see during life of the organism, owing 

 to the densely granular cytoplasm. In fixed preparations it may 

 be seen to have a delicate membrane studded internally by chroma- 

 tin granules, and with a minute homogeneous endosome (Fig. 171). 



