9 



material soluble in water. They do this very frequently when 

 walking about over a clean glass, possibly with the idea of 

 extracting nourishment from it. A fly after a good meal may 

 often be seen blowing fluid bubbles from its trunk, and 

 sucking them in again, as in the diagram, Fig. 5, perhaps 

 for practice. 



Carriage of Bacterial Infection by Hies. 



From the above account it is clear that there are a priori 

 reasons for suspecting the fly of carrying bacterial infection. 

 Born in a dunghill, it spends its days flitting between the 

 sugar basin, milk-pan, and any fascal matter available. Its 

 hairy, probably sticky, feet, and the habit of regurgitating 

 the contents of the crop and defecating at frequent intervals 



FIG. 5. 



A fly blowing bubbles. 



suggest it to be an excellent inoculating agent for any 

 bacteria it may pick up in the satisfaction of its unsavoury 

 tastes. 



That it does, indeed, operate in this way has been 

 abundantly demonstrated. Flies which have wandered over 

 cultures of organisms and afterwards been allowed to walk 

 upon sterile agar plates, leave a rich crop of germs as their 

 footprints, which can be demonstrated by subsequent in- 

 cubation. Castellani (1907) transferred yaws to monkeys in 

 an analogous way. 



The carriage of infection in the alimentary canal and its 

 deposition by regurgitation or fasces has also been shown 

 over and over again (Grassi (1883), Macldox (1885), Alessi 

 (1888), Celli (1888), Sawtchenko (1892), Uffelmann (1892), 

 Yersin (1894), Nuttall (1897), Firth and Horrocks (1902), 

 Manning (1902), Hay ward (1904), Lord (1904), Chantemesse 

 (1905), and Buchanan (1907) ). 



These modes are probably more important than the 

 carriage of bacteria upon the exterior. Many pathogenic 



