730 PATHOGENIC PROTOZOA 



are clear, glassy and evidently viscid and dense and have given it its 

 name "histolytica, " since Schaudinn states that he saw the ameba 

 penetrate the mucous membrane, the pseudopods dissecting apart the 

 epithelial cells. The nucleus, when the endoplasm is packed with in- 

 clusions, may not be visible, but further search will reveal amebse 

 showing a nucleus. It is vesicular, with a delicate limiting membrane, 

 and as it is highly refractile, may appear as a clear bright spot. As 

 the specimen grows older the ameba3 lose much of their motility and 

 the nucleus may become clearly visible, revealing small chromatic dots 

 or masses adherent to its inner surface and a small central karyosome. 











FIG. 159. END AMEBA HISTOLYTICA. FIG. 160. ENDAMEBA HISTOLYTICA 

 (Army Med. School Collection, Wash- (X 1150.) (Army Med. School 



ington, D. C.) Collection, Washington, D. C.) 



The cysts are round, quite small, about 10 microns, and show four 

 small ring-like nuclei ; the wall is distinct and often double-contoured. 



The motile amebae cannot be confused with anything else, but when 

 in the resting stage they have been mistaken for swollen and edematous 

 epithelial cells. A little attention to the nucleus will prevent this 

 error, since the tissue-cell nucleus is large, distinct, and entirely dif- 

 ferent from the nucleus of an ameba. 



In specimens stained with hematoxylin the finer details, especially 

 in the nucleus, may be studied, but stained preparations are never nec- 

 essary for clinical diagnosis. In smears from fresh cases vegetative 

 forms only are found, later many degenerative forms appear and dur- 

 ing convalescence only cysts may be seen. In stained specimens there 



