1058 PATHOGENIC PROTOZOA 



distilled water to one of the iron-alum solution is satisfactory), until 

 the slide under the microscope shows the structure of the nucleus; 

 the examination is made in water under a cover glass. 



7. When the differentiation is complete the slide is washed in 

 distilled water and passed through graded alcohols, 80, 95 and 

 absolute into xylol and xylol-balsam. This stain is permanent. 



Romanowski stains on dried smears may be used, but are not so 

 good. 



In fresh specimens Entamoeba histolytica presents the following 

 appearance: the vegetative forms are pale, unstained with bile, and 

 are seen to be large bodies, 20 to 30 microns in diameter, consisting 

 of endo- and ectoplasm, and often showing a delicate nucleus and 

 also many inclusions in the digestive vacuoles, principally red blood 

 cells. The organisms for several hours after the stool is passed 

 remain actively motile, pushing out clear, glass-like pseudopods, into 

 which the granular endoplasm pours as the amoeba progresses across 

 the field. Even when there is no progression the pseudopods are 

 protruded or retracted first in one then in another direction. There 

 is usually, during motion, a distinct separation of the clear ectoplasm 

 from the granular endoplasm, and the latter, in acute cases es- 

 pecially, contains many red blood cells, occasional examples show- 

 ing as many as twenty or thirty. The presence of red blood cells 

 either entire or partly digested is characteristic of Entamoeba his- 

 tolytica. The amoeba is sometimes greenish, and it is supposed that 

 this color is due to hemaglobin liberated from the ingested red cells. 

 The pseudopods of this species are clear, glassy and evidently viscid 

 and dense and have given it its name "histolytica," since Schaudinn 

 states that he saw the amoeba penetrate the mucous membrane, the 

 pseudopods dissecting apart the epithelial cells. It is much more 

 probable however, that the parasite secretes a strong ferment, which 

 first softens and then dissolves the tissue cells. The nucleus, when 

 the endoplasm is packed with inclusions, may not be visible, but 

 further search will reveal amoebae 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 amoebae 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 karyosomo. 



The motile amoebae cannot be confused with anything else, but 

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



