DIENTAMCHBA FRAGILIS 



(1927). Apparently moisture and a suitable temperature 

 are the required stimuli ; cysts in a weak saline solution 

 on a slide under a cover glass when maintained at a 

 temperature of 37° C. for about 5 hours were seen to 

 excyst on a number of occasions. When injected into the 

 stomach of guinea-pigs cysts are carried into the small 

 intestine where they may excyst in the jejunum within 

 a period of three hours. 



4. DIENTAMCEBA FRAGILIS 



Only a few cases of infection with this species are on 

 record, and cysts have been reported by only one observer 

 (Kofoid, 1923). The rarity of cysts and the apparent 

 delicacy of the trophozoites probably account for the 

 small number of infections that have been noted ; in fact, 

 its seems strange that this species can continue to exist. 

 It has been suggested that man is not the "normal" host 

 of D. fragilis, but no one has yet discovered this or 

 similar species in any lower animal. Obviously no discus- 

 sion of its host-parasite relations is possible until further 

 data are obtained. 



5. endamcEba gingivalis 



Transmission. Although E. gingivalis is probably not 

 pathogenic, as once supposed, it is of considerable interest 

 because its habitat differs from that of all other amoebae 

 of man. It has been suggested that this form and E. 

 histolytica belong to the same species, but recent studies, 

 especially those of Kofoid and Swezy (1924c), render 

 this highly improbable. Cysts have been described but 

 there is no evidence that they really exist although Wen- 



125 



