146 THE HOUSE FLY— DISEASE CARRIER 



Sykes*s observations in his own home city, but never- 

 theless Doctor Chapin is a well-known man of high 

 scientific standing and his conclusions must be viewed 

 with all respect. When we come to analyze the situa- 

 tion, however, it becomes at once apparent that in cities 

 the correlation or non-correlation of the curve of house 

 fly abundance and of the abundance of typhoid has 

 practically no effect upon our conclusions as regards 

 the possible transfer of the disease by flies. 



Flies are numerous at all times during the summer, 

 and wherever excreta carrying virulent germs can be 

 reached by them it is sure to be covered by them — 

 whether in early June or in October — and the chances 

 are almost as great that food supplies will be reached 

 by these flies whether there are 500 of them or 600 of 

 them. The fact that typhoid fever does not develop 

 in localities where flies are most numerous does not 

 mean that it is not carried by flies, but simply means 

 that the flies in that locality have had no opportunity 

 to visit substances containing virulent germs. A cor- 

 relation of the two curves in question has been found 

 by Doctor Jackson in his report to the Merchants' As- 

 sociation of New York, and it has been found by Cap- 

 tain Ainsworth in his studies of the house fly and 

 enteric fever in India, by Purdy (19 10) in New 

 Zealand, and by Osmond (1909) in Cincinnati, and 

 where it is coincident it may serve to attract the atten- 

 tion of people to the subject, but the absence of the 

 correlation in any given case is a most inconclusive ar- 

 gument. 



