INSECTS AND HUMAN DISEASE 123 



was turned to house flies, and in the bodies of many of 

 these insects, taken from houses where there were children 

 ill with infantile enteritis, the germs of the disease were 

 found. 



" But because infected flies were found after the onset of 

 the cold weather in the autumn, and because some infected 

 flies were found in a house in the country where no child 

 suffering from the disease happened to be discovered, and 

 because some doctors believed that the fly curves and the 

 disease curves do not correspond, this research seems to 

 have been relegated into the background. It should have 

 been named as one of the most important investigations of 

 the present century. Flies may live for weeks in the cold 

 weather in fact, we know they do ; but the majority die. 

 And there may be enteritis-carriers, as we know there are 

 typhoid-carriers, who appear apparently healthy and who 

 have had but mild attacks of the disease." So little notice, 

 however, was taken of the established connection between 

 house flies and disease that in the summer of 1911 infantile 

 enteritis broke out again nearly all over England ; thousands 

 of pounds were spent in a vain attempt to stern the tide of 

 mortality, flies were everywhere, thriving in the decaying 

 organic matter which the hot weather made plentiful, yet 

 no one, apparently, gave any thought to a campaign for 

 stamping them out and so mitigating the evil. In America, 

 bacilli were discovered, similar to those discovered by 

 Morgan, and equally pathogenic. 



Various estimates have been made as to the number of 

 bacteria that may be carried about the body of a single 

 healthy, active fly; one investigator, Torry, puts the 

 number at twenty-eight million in its intestine, and four 

 and a half million on the outer surface. Esten and Mason, 

 by careful experiment, found that the number of external 

 bacteria varied from five hundred and fifty to over six and 

 a half million; other observers have put the number as 

 high as five hundred million per fly. The numbers seem 



