PART IV. CARRIAGE BY HOUSE-FLIES 137 



with developed oocysts of the human isospora. No infection took 

 place. An isospora is found very commonly in Alexandria cats, but 

 the oocyst is quite unlike that of the human parasite. The oocysts 

 of the cat isospora resemble those of the European form. 



(2) A mouse was fed repeatedly with developed oocysts and no 

 infection took place during an observation of over four months. 



Observations on Lizards. A number of lizards which lived in 

 open spaces in Alexandria were examined. Two distinct types 

 were dissected. One of these (Agama sp.?) is very common in 

 stony places, where it lives on flies and also appears to feed upon 

 vegetable material. In this amongst other protozoa were found a 

 tetramitus and an amoeba which resembled E. coli not only in its 

 free stage but also in the production of an eight-nuclear cyst 

 indistinguishable from that of E. coli. The other lizard was a 

 skink which lived in sandy places. It fed exclusively on insects. 

 There were numerous flagellates in the gut but none resembling 

 those of the human intestine. It seems just possible that lizards 

 might become infected with human parasites by feeding on flies 

 which had already fed on human faeces. 



(2) Flies as Carriers of Intestinal Protozoa and other Infections. 



The relation of house-flies to the human intestinal protozoa and 

 the possibility of their dissemination by flies which have fed on 

 infected faeces has been discussed by us in two earlier publications. 

 {Memorandum on the carriage of cysts of E. histolytica by house- 

 flies, with some notes on their resistance to disinfectants and other 

 agents, issued by the Medical Advisory Committee, Mediterranean 

 Area, April, 1916, and the same with additional notes on a more 

 -extended examination of wild flies, in the Journal of the Royal 

 Army Medical Corps, May, 1917.) 



We have shown that flies which feed on faeces containing th^ 

 free or encysted protozoa readily take these into their intestine. 

 By dissecting flies at various intervals after feeding we have noted 

 that so long as any of the faeces remained in the gut the encysted 

 forms could be found. 



The following is a record of some of our observations. In these 

 nothing of a doubtful nature has been accepted as evidence of the 

 presence of a cyst of one of the intestinal protozoa. We have care- 

 fully ignored anything which was not absolutely certain, so that 

 our finds in the examination of wild flies are somewhat lower 

 than was actually the case. 



(a) Flies fed on Infected Faces and dissected later. (I) Six 



