PART IV. CARRIAGE BY HOUSE-FLIES 141 



the Journal of the Royal Anmj Medical Corps, May, 1917, is 

 reprinted on pages 149-155, but some further explanation of the 

 methods employed will be given here together with some additional 

 observations. 



The majority of the flies were examined singly, though some 

 were examined in batches. When examined singly, the fly was 

 caught in a glass tube (2 by 1 inches), and the tube was placed 

 on the laboratory bench standing with the open end on a glass 

 slide. No food was given to the fly, which deposited droppings 

 either on the sides of the tube or on the slide. The total number 

 of the droppings deposited by the fly, the number of droppings on 

 the slide, and the length of time since capture were noted. Only 

 the droppings on the slide were examined. In most cases these 

 were dry when examined, but the drying did not interfere seriously 

 with the identification of the objects present. The examination was 

 carried out by running some saline solution on to the slide, and 

 placing over the droppings a cover-glass. The droppings were then 

 examined with the f and -inch objective without disturbing them. 

 A gentle tap on the cover glass then caused the droppings to spread 

 out slightly, when such objects as worms' eggs could be detected. 

 From one large dropping there emerged in this manner two lateral- 

 spined bilharzia eggs. Finally, the cover-glass was moved, so that 

 the droppings were completely emulsified in the saline, and search 

 was made with the % and j^-inch objectives for cysts of protozoa 

 and other objects. It is evident that any eggs or cysts discovered 

 in this manner must have passed through the intestine of the fly. 

 The view that any of the cysts or eggs found had been transported 

 on the legs of the flies is hardly tenable. As far as the worms' eggs 

 are concerned, these were always found in the droppings themselves 

 before they had been completely emulsified in the saline and this 

 was true most usually of the cysts also so there is very little 

 likelihood that any of the objects found had been deposited by 

 the flies' legs on the slide between the droppings. 



As already stated, doubtful objects were ignored, and, for the 

 identification of the cysts, iodine solution was often used by 

 drawing it under the cover-glass by means of blotting-paper. 



We have given our method of examination. in some detail, 

 because some other observers who have examined flies have relied 

 upon dissection of the gut, and quite recently Shircore, who has 

 examined flies for worms' eggs in Mombassa Hospital, employed a 

 method which involved emulsifying the organs of the flies, and 

 centrifuging after addition of ether. The examination of droppings 



