Xll. INTRODUCTION 



the animal which not only constantly dines with us, tests 

 the wholesomeness of our food and of the food of our 

 children, but also regales its palate with the juices of the 

 excremental products of various animals, including man. 

 Constant in its attendance upon us in our sleep which is 

 often disturbed and when awake, we are apt to lose sight 

 of that side of the fly's life, of its double life, which is 

 passed out of doors, most frequently in search of a place to 

 deposit its eggs, which is equivalent to saying in search of 

 excrement or decaying vegetable substances. 



It has been tried and found guilty in spite of the 

 questionings of those who maintain the doctrine that every 

 creature performs some useful purpose. Undoubtedly the 

 fly does, for where there is an abundance of filth, there will 

 the flies gather together, there will they multiply and 

 increase. Its function to-day is nothing more or less than 

 a danger signal to indicate insanitary conditions and the 

 presence in the neighbourhood of decaying or excremental 

 substances. Abolish these and the breeding places of the 

 flies will be eradicated; maintain them and this potential 

 disease carrier will be retained within our houses. 



The importance of the house-fly as a disease carrier is 

 considered at length in the third part of this monograph 

 and in Appendix A., and I have considered briefly the 

 preventive and remedial measures in Appendix C. It will 

 never become a rare insect, and the vision of my friend Sir 

 James Crichton Browne of the aged person showing the 

 wondering child the only specimen existing of the house-fly 

 in the British Museum will, unfortunately, never be 

 realised ; but there is no reason why, by the adoption of such 

 sanitary measures as the breeding habits of the insect have 

 indicated to be necessary, it should not be considerably 

 decreased in numbers and rendered impotent as a disease 

 carrier. We need such determination and zeal on the part 

 of public bodies as that displayed by the New York 



