456 PROTOZOOLOGY 



vacuolated, and contains ordinarily a large number of pale greenish 

 bodies (which are probably nuclei of leucocytes, pus cells or other 

 degenerating host cells) and bacteria in food vacuoles; nucleus, 2-4/x 

 in diameter, appears as a ring ; when stained it shows a small central 

 endosome and small peripheral granules closely attached to the 







Si 



~Qm -V-. <#** 



m 



A 



« 



Fig. 193. Entamoeba gingivalis, X1150 (Kudo). 1, 2, living amoebae; 

 3-7 stained amoebae. 



membrane. Stabler (1940) observed 5 chromosomes during binary 

 fission. Encysted forms have not been observed in this amoeba. 

 Kofoid and Johnstone (1930) reported having seen the same organ- 

 ism in the mouth of monkeys (Rhesus and Cynomolgus) from south- 

 east Asia. 



E. gingivalis is the very first parasitic amoeba that has become 

 known to man. Gros (1849) found it in Russia in the tartar on the 

 surface of the teeth. Some observers maintain that this amoeba is the 

 cause of pyorrhoea alveolaris, but evidence for such an assumption 

 seems to be still lacking. It has been found in the healthy gums and 

 even in false teeth (Lynch). Therefore, it is generally considered as 

 a commensal. It is widely distributed and of common occurrence. 



In the absence of the encysted stage, it is supposed that the 

 organism is transmitted in trophic forms. According to Koch (1927) 

 who studied the effects of desiccation and temperatures upon the 

 amoeba in culture, the amoeba is killed at 0°C. in 18 hours, at 5°C. 

 in 24 hours, at 10°C. in 48 hours, at 45°C. in 20 minutes, at 50°C. in 

 15 minutes, and at 55°C. in 2 minutes. At 40°C, the survival is said 

 to be for an indefinite length of time. Complete desiccation of the 

 culture medium or immersion in water at 60°C. kills the amoeba. She 



