160 THE HOUSE FLY— DISEASE CARRIER 



have doubtless had opportunity of feeding on and be- 

 coming contaminated with excremental material of 

 human origin, may have been a means of carrying in- 

 fected material to certain foodstuffs, such, more par- 

 ticularly, as milk and sugar, and so, indirectly, of 

 bringing about infection of the human subject.' 



"Snell (1906), Medical Officer of Health, Coventry, 

 is stated by Ainsworth (1909) to have shown that 

 seventy per cent, of the 'cases of infantile diarrhea oc- 

 curred in the northeast part of his district, close to a 

 large collection of refuse where flies swarmed.' 



"Sandilands (1906, p. 90) considers that there are 

 'good grounds for the supposition that in this disease, 

 which in some respects is analogous to typhoid fever 

 and cholera, flies may be carrying agents of the first 

 importance.' He notes that the meteorological condi- 

 tions which influence the prevalence of diarrhea 'exer- 

 cise a precisely similar effect upon the prevalence of 

 flies. 



" 'The immunity of well-to-do infants may be ex- 

 plained partly by the distance that separates the sick 

 from the liealthy and partly by the small number of 

 flies in their neighborhood. In poorer districts six or 

 seven babies may occupy the tenements of one house 

 with a common yard where the flies congregate and 

 flit in and out of the open windows, themselves con- 

 veying infected excrement to the milk of healthy in- 

 fants, or depositing the excrement in the dust-bin, 

 whence it may again be conveyed into the house by 

 other flies. Calm weather promotes diarrhea, and high 



