INTRODUCTION. 



" Familiarity breeds contempt." This, until a few years 

 ago, was certainly the case with regard to man's attitude 

 towards the house-fly, and it not infrequently happens that 

 some animals are so common that they are not considered 

 of sufficient scientific interest to be worthy of study. It is 

 unfortunately too often considered by zoologists, probably 

 unknowingly, that the ultimate value of the careful study 

 of an animal is directly proportionate to its rarity. A 

 little reflection will afford other instances of the neglect 

 of common creatures. 



Of all animals associated with man, none is more common ; 

 ho has no attendant more constant. Wherever he has 

 travelled the ' domestic ' fly has accompanied him, by water 

 and by land; whether he travels on the modern ocean liner, 

 on the Canadian Pacific trans-continental express making 

 its three thousand miles journey, or in the humble electric 

 car from street to street, house-flies are his constant 

 companions. 



Recent investigations, however, have shown that we must 

 substitute " fear " for " contempt " in the old adage in the 

 case of this ubiquitous companion. The house-fly is not " a 

 wholesome little creature" as it was described by one whose 

 scientific knowledge is as profound as it is accurate (I refer 

 to an editorial published in a well-known and much- 

 advertised English journal commenting on a lecture that 

 was delivered by me a few years ago on the dangers of the 

 house-fly), but it is an animal which normally bears on its 

 feet, legs and body and leaves in its tracks the organisms 

 productive of decay and not infrequently disease. This is 



