8 



HOUSEHOLD INSECTS 



over which a fly was allowed to walk. In every foot- 

 print there is a white colony of bacteria with millions 

 of individuals. 



Esten and Mason examined 414 flies from different 

 sources and found that the number of bacteria carried 

 by each one varied from 550 to 6,600,000, with an average 



Fig. 5. 



Plate of gelatine, showing colonies of bacteria in footprints 

 of fly. (XI.) 



for each fly of nearly one and one-fourth millions. They 

 also found that those flies caught in swill-barrels, pig-pens, 

 and similar places carried the most bacteria and the most 

 objectionable kinds of bacteria. 



The mouth-parts of the house-fly are very complicated 

 but, in general, they constitute a short proboscis fitted 

 for sucking but not for piercing. The house-fly cannot 



