PART IV. CARRIAGE BY HOUSE-FLIES 145 



The observations recorded demonstrate the importance of all 

 measures directed against the flies, their capture and destruction 

 and the removal of every possible breeding place. It is perhaps of 

 interest to record here the fact that one of the large fly-traps 

 designed by Lieutenant-Colonel Balfour, C.M.G., K.A.M.C., was 

 put up in the hospital compound near the cook-house. It had a 

 marked effect in reducing the number of flies which entered the 

 cook-houses, and this can easily be understood when we realize 

 that a catch of forty-eight hours yielded one and three-quarter 

 pints of flies. A count was made and it was found that one pint 

 of flies (mostly Musca, with an admixture of larger forms such as 

 Calliphora, Lucilia, Sarcophaga, etc.), numbered a little over ten 

 thousand. Furthermore, many of the flies recorded in the table 

 above as being infected, were actually caught either inside or as 

 they were about to enter the fly-trap. 



Conclusions regarding the Fly Question. 



(1) Flies feeding on faeces readily take up encysted and other 

 forms of protozoa into their intestine. 



(2) The encysted forms of the protozoa can be found in the 

 fly's intestine so long as any faecal matter remains there. If the 

 flies are prevented from feeding this may be as long as forty-two 

 hours. If the flies are feeding constantly off various materials the 

 later feeds tend to clear out what has been taken up before, so that 

 the time becomes shorter. 



(3) The cysts do not degenerate to any extent in the gut of 

 the fly. 



(4) Flies can deposit in their own droppings material they have 

 ingested only five minutes before. Live trichomonas were found 

 in the faeces of a fly which had only fed five minutes before. 



(5) Cysts of protozoa (and eggs of worms) can readily pass 

 unaltered through the intestine of the fly. 



(6) Under natural conditions, if flies have access to infected 

 faecal material (cysts of protozoa or eggs of worms) a large 

 percentage of the flies taken in the neighbourhood, as proved by 

 the examination of their droppings, will be found to have the 

 infectious material in the gut and a still larger proportion will be 

 found to have fed on faecal matter. 



(7) Flies becoming infected in this way will naturally deposit 

 the material on any kind of food on which they feed, and it seems 

 that the wide distribution of human protozoal infections in warm 

 countries can best be explained in this way. 



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