APPENDIX A 1*78 



and also, I have found, on the state of the weather and sky. 

 If the flies therefore become less active, they will be less 

 liable to transmit the organisms causing summer diarrhoaa, 

 and although the numbers caught in the houses may exceed 

 in numbers those caught earlier in the season when the 

 diarrhosa curve was rising, those which are very active will 

 be less in number and consequently instead of increasing, 

 the diarrhoea curve begins to fall. The dissemination of 

 summer diarrhoaa is brought about chiefly owing to the 

 activity of the flies outside the houses as well as inside. A 

 fall in temperature or a spell of dull weather decreases 

 considerably this outside activity and will therefore cause a 

 decline in the number of diarrhoea cases. The number of 

 cases of diarrhoea is dependent on the activity of the flies 

 and this is dependent on climatic conditions, chief of which 

 is temperature. Considered in the light of these facts this 

 seeming difficulty is not an argument against the idea that 

 we hold on the relation of flies to summer diarrhoea, but 

 rather one in support of it. 



II. BACTERIA AND FUNGAL SPORES CARRIED BY MUSCA 



DOMESTIC A. 



In the summer of 1908 my friend Mr. H. T. Gtissow, 

 Dominion Botanist of Canada, made three extremely inter- 

 esting and instructive experiments with a view to discovering 

 the kinds of organisms which the house-fly may normally 

 carry, and he has kindly allowed me to give his results, 

 hitherto unpublished, here. 



Experiment No. 1. 



A fly was caught in his living room (Norwood, London) 

 at 10 a.m. on May 4th and allowed to walk over nutrient 

 agar-agar in a Petri dish; the necessary precautions being 

 taken to prevent extraneous infection of the medium. The 



