CARRIAGE OF DISEASE 161 



winds are unfavorable to the spread of diarrhea and to 

 the active migration of flies ahke. Loose soil and fis- 

 sured rock, containing organic filth in its crevices, favor 

 the spread of diarrhea and the breeding of flies, whilst 

 solid rock is unfavorable to both.' (See also News- 

 holme, 1906, p. 145.) 



''Hamer (1908), who has studied the relation of fly 

 prevalence (Mttsca, Homalomyia) to diarrhea from an 

 epidemiological point of view, appears to be somewhat 

 sceptical as to flies being active agents in the spread of 

 infection. He considers that the increase in flies and 

 diarrhea may be due simply to a coincidence. 



^'Ainsworth (1909, p. 498) has studied the relation 

 of infantile diarrhea to flies in Poona and Kirkee, India, 

 and illustrates the relation by means of a yearly curve 

 which is very striking as affording evidence that flies 

 stand in causal relationship to diarrhea. 



"All authorities agree that flies rest under strong 

 suspicion of serving as disseminators of diarrheal in- 

 fection." 



Jackson (1907) gives the results of numerous ob- 

 servations upon the relation of flies to intestinal dis- 

 eases (including infant diarrhea) and the relation of 

 deaths from intestinal diseases in New York City to 

 the activity and prevalence of the common house fly 

 is indicated not only by repeated observations but also 

 by an interesting plotting of the curve of abundance 

 of flies in comparison with the plotted curve of the 

 abundance of deaths from intestinal diseases, indicat- 

 ing that the greatest number of flies occurred in the 



