O INTRODUCTION 



In the following chapters the information at present available 

 on the habits and life-histories of non-biting flies, their capacity 

 for carrying and distributing bacteria and parasitic ova, and 

 their relation to various diseases is discussed, and the more 

 important experimental evidence is given in detail. The reader 

 can therefore make himself acquainted with the methods which 

 have been adopted and the results which have been obtained, 

 and perhaps gather some indications as to the lines on which 

 future investigations should proceed. 



Technical descriptions of species and details of bacteriological 

 experiments are given in small type. 



Several of the diseases, typhoid fever, cholera and infantile 

 diarrhoea, which the house-fly is reputed to spread, are important 

 ones. The problem of its relationship to such diseases can only 

 be solved by the combined efforts of observers in various fields 

 of work, and in different countries. Certain aspects of the 

 problem must be left to specialists in entomology, bacteriology, 

 mycology and helminthology, but sanitary officers, medical men 

 and workers, who are not specialists in any of these branches of 

 study, may render most important assistance. In every branch 

 careful, prolonged and accurate study, with minute attention to 

 details is necessary, but more particularly is this the case in 

 regard to bacteriology. The difficulties attending the isolation 

 and identification of pathogenic bacteria, particularly those 

 belonging to the typhoid-colon group, from ' wild ' flies are 

 especially great, since allied, almost indistinguishable, types are 

 frequently present in the intestines of flies. No diagnosis should 

 therefore be accepted unless all the known tests for identification 

 have been applied (see Chaps, xil, xiv). 



With the knowledge now at our disposal of the habits of 

 house-flies it should not be impossible to greatly diminish their 

 numbers in some selected areas, where epidemic diarrhoea is 

 usually prevalent, and thus definitely prove whether they are 

 mainly responsible for the spread of this disease, or not. If 

 they are proved to be responsible the application of suitable 

 measures would save many thousands of lives annually. 



Apart from the question of epidemic diarrhoea measures 

 directed against flies and their breeding places would undoubtedly 



