124 '""E AMOEBAE LIVING IN MAN 



organism then appears under the microscope as a delicate ring of proto- 

 plasm, containing the two nuclei and any food inclusions which may 

 have been present, with a large space in the middle. At this stage it has 

 a striking resemblance to a Blastocysiis. Degenerating organisms may 

 remain in this condition for a long time before they finally disintegrate. 



Although a prolonged and very careful search has been made for the 

 cysts of this organism, none have ever been found. In this respect 

 D./ragilis resembles E. gingivaiis. How the former is transmitted from 

 host to host is still a matter for speculation. Only when the stools of 

 an infected individual are liquid or soft can the amoeba be found in 

 them. When they are hard and formed, no trace of the amoeba, and 

 no resistant stages, can be detected. The free amoeba usually perishes 

 so rapidly outside the body that it is highly improbable that it can be 

 transmitted in this form. 



The habitat of D.fragilis is probably the colon, but up to the present 

 it has been found only in the stools. It is not known to occur in any 

 animal but man, and has not yet been cultivated. 



To judge from the food contained in its vacuoles, D. fragilis lives 

 exclusively on bacteria and other small vegetable micro-organisms in 

 the gut contents. It is therefore, in all probability, a harmless com- 

 mensal like E. coli and £. nana. No method of treatment is known to 

 have any effect upon it. 



The geographical distribution of this remarkable and interesting 

 organism is at present uncertain, but it seems probable that it is wide. 

 Of the seven cases of infection which I have studied, one was in a 

 healthy resident in Great Britain, who had never been abroad ; two were 

 in British soldiers invalided home to England from Salonika, suffering 

 from dysentery ; one was in a British soldier invalided from Salonika to 

 England with malaria ; and the remaining three cases were New Zealand 

 soldiers who had served in France and England only. Although most 

 of these cases had suffered from dysentery, there is no evidence that it 

 was in any way due to infection with D. fragilis : and none of them 

 were suffering from dysentery at the time when their infections were 

 discovered. 



