METHODS BY WHICH BACTEIUA AllE .Sl'KEAD 221 



dancing attendance in Hygcia, liu said we should luuk ii|»nii tlicni 

 as winged sponges spreading hither and t hither to carry out i hf foul 

 behests of Contagion, ^rany others have called attention t(j the 

 general facts and also their connection with specific diseases; the 

 latter authorities will be mentioned in considering the various 

 diseases. Of the former the following may be mentioned : Hewson 

 (1871), Cobbold (1879), Megrun (1875), Laboulbene (1875), White 

 (1880), Slater (1S81), Grassi (1883), Taylor (1883), Moore (1893), 

 Coplin (1899), Parker (1902), Martini (1904), Bergey (1907), Scott 

 (1909), Skinner (1909) and others (see Bibliography). 



Methods by which Bacteria are spread by^ Flies. 



In discussing the relation of house-Hies to disease the various 

 methods by which they are able to distribute the pathogenic and 

 other bacteria must be borne in mind. It has generally been 

 understood that the mechanical transference of bacteria and other 

 micro-organisms on the exterior of the fiy, that is on its body 

 and appendages, was sufficient to account for the distribution of 

 infection. In the experimental evidence which is quoted in the 

 succeeding sections this assumption has generally been made by 

 the investigators. Now while this is true in many instances, there 

 is very strong evidence derived from careful experiments that the 

 infection from the exterior of the fly is far from being the sole 

 method of bacterial distribution. 



Flies which frequent infectious matter not only inevitably con- 

 taminate the exterior of their body and their appendages, but by 

 feeding upon such matter, which is one of the two reasons for their 

 visiting it, they take the bacteria and other organisms which it 

 contains into their alimentary tracts. In consequence the crop, 

 the stomach and the intestines become the temporary resting 

 places of the bacteria. In the gut of the fly the micro-organisms, 

 especially those of a non-spore-producing kind, will naturally 

 remain in a viable condition for a considerably greater length of 

 time than on the exposed external surface of the insect, and the 

 period during which infection may be distributed will be length- 

 ened. In treating of the various pathogenic organisms I shall 

 have occasion to quote many instances of the last fact. 



