GENERAL BIOLOGY 



PATHOGENIC PROTOZOA 



Class I. Rhizopoda 



(a) Entamoeba hystolytica (also called entamoeba dysenteriae 

 (Fig. 54). 



Entamoeba histolytica causes a chronic ulcerative process in 

 the large intestine, so-called amoebic dysentery. The organisms are 

 frequently carried to the liver by the portal circulation and give rise to 

 abscesses which may attain a large size and may extend to a pleural 

 cavity or to a lung. 



It is a common infection in the tropics, but occurs 'also more 

 or less frequently in temperate zones. 



The organism measures fifteen to twenty-five micra in diarn- 



Entamoeba gingivali 

 1914). 



(buc calls) . 



Fig. 55. 

 (After A. J. Smith in Dental Cosmos, Sept., 



eter. It contains a small round vesicular nucleus which stains but 

 poorly with the ordinary basic dyes and with alum hematoxylin. The 

 nucleus contains a minute nucleolus. The cytoplasm around the nucleus 

 is finely granular and is surrounded by an outer zone or ectosarc which 

 is transparent and refractive, and which sharply defines the outer limits 

 of the organism. 



The entamoeba hystolytica is examined on a warm stage, in 

 order to detect the characteristic movements ; but it is readily identified 

 in properly fixed tissues owing to its characteristic morphology. 



"The organism is quite phagocytic and frequently contains red 

 blood corpuscles, bacteria, or cellular debris. It is able to penetrate 

 fibrous and other tissues and is frequently found in the walls of blood 

 vessels and inside of them." 



It secretes a mild toxin (which may be a waste product) which 

 'slowly kills the cells in its neighborhood and then gradually dissolves 

 them. 



Amoebae are, however, often found in normal tissues. Some- 

 times the nuclei seem to be fading out. 



It is found principally in the intestines and sometimes in the 

 liver. 



Cultures of these amoebae have been shown to withstand dry- 

 ing from eleven to fifteen months. 



(b) Entamoeba buccallis (also called E. gingivalis and E. den- 



