236 



ANIMAL PARASITES 



killed at low temperatures, and resist up to 6oC. when in the 

 encysted state. Quinine, permanganate of potash, weak acid and 

 silver nitrate are quickly fatal to vegetative forms. Emetin is 

 a useful drug since it kills all but encysted forms after a very 

 short exposure if direct. 



Entamceba tetragena, formerly classified as a separate variety, 

 is now generally believed to be but one stage in the development 

 of Ent. histolytica. 



In stools (from dysenteric cases) over a day old, amoebae are 

 not often found, as they undergo a rapid disintegration outside 

 the body. 



Amoebae are cultivated upon stiff agar preferably with defibri- 

 nated blood and in company with bacteria. If a colony can be 

 obtained free of bacteria, development will continue on agar 



FIG. 73. Entam&ba tetragena. The same living individual drawn at brief 

 intervals while moving. (From Doflein after Hartmann.) 



smeared with organ extracts. The addition of dead bacteria to 

 culture media seems favorable to their development. The poisoi 

 is not known. The free amoebae in the colon are easily killed, bul 

 when encysted are more resistant. Quinine is fatal to cultures ii 

 ten minutes in strength of 1-2500. Formalin is not practicable. 

 Endamoeba buccalis is found in the mouth especially in carioi 



