264 THE RELATION OF FLIES TO SUMMER DIARRHOEA 



flies and the distribution of cases of infantile diarrhoea, Martin 

 states, and I think justly: "I doubt very much whether any 

 evidence of great value could be obtained upon this point. Even 

 supposing it to be true that fly carriage is of first importance, 

 I should expect that, if all the facts were known, a much higher 

 correlation would be discovered between diarrhoea and carelessness 

 with regard to disposal of excreta and protection of food from the 

 visitation of flies than between diarrhoea and fly prevalence." 



As a conclusion to this resume of the evidence for and against 

 the hypothesis that the house-fly is an important agent in the 

 dissemination of summer diarrhoea, in regard to which idea a 

 critical attitude is, in my opinion, not only justified but conducive 

 to a more satisfactory elucidation of the problem, I do not think 

 I can do better than to quote Martin's concluding paragraph. He 

 says : " Many of the facts which I have brought forward merely 

 indicate some form of infective agent and do not necessitate 

 recourse to the hypothesis that carriage of flies dominates the 

 situation. I would point out, however, that: 



" 1. The fly-carrier hypothesis is the only one which offers 

 a satisfactory interpretation of the extraordinary dependence of 

 the epidemic upon the accumulated effect of temperature. 



" 2. That it offers a ready explanation of the spread of infection 

 to neighbouring children who have no direct personal contact with 

 the patient. 



" 3. That the peculiarities of the relation in time between fly 

 prevalence and the epidemic in different localities are not incon- 

 sistent with the view that fly carriage is essential to epidemicity. 

 No other interpretation which is at present forthcoming is nearly 

 so satisfactory, and it is at least worth}^ to guide in the meantime 

 our efforts at prevention \" 



1 In a recent Bulletin Armstrong (1914) gives an account of an effort made in 

 the summer of 1913 by the Department of Social Welfare of New York to determine 

 the imj)ortance of the house-fly in the transmission of diarrhoeal disease among 

 infants. Two congested areas in the Italian quarter were selected. In one every 

 step was taken to make the houses sanitary and fly less by education, screening, 

 cleaning up, etc. ; in the other nothing was done. A careful census and weekly 

 inspections were made. The statistical findings, if not entirely conclusive, were 

 exceedingly interesting and demonstrated an apparent marked i-eduction in the 



