342 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 9 



(1,260 yards from the station) and 40,237 from the Laboratory (830 

 yards from the station). Do not the respective totals of seventy-four 

 and twenty-six flies recovered from these release points bear a more 

 direct relation to the comparative distances and numbers released 

 than to any consideration of wind direction or wind velocity that can 

 be deduced? A similar review of the data concerning the other two 

 release points gives no essentially different results. This seems to 

 indicate, then, that as a stimulus having any effect on ultimate dis- 

 persion in a given direction from a breeding area when a long period 

 of time is concerned, wind may be a negative factor, and in this par- 

 ticular citation there is no evidence to demonstrate any influence of 

 wind as a stimulus when the shorter periods of time concerned are 

 considered. 



If Hindle's idea of dispersion against and across the wind has a true 

 significance in the economy of fly dispersion, it would seem capable of 

 interpretation in the following way. Without the assistance of air 

 currents, odors originating at any given point have the ability to dif- 

 fuse through the atmosphere and within a certain radius would logically 

 be sufficiently concentrated to serve as a positive chemotropic stimu- 

 lus. A point must eventually be reached, however, at which the diffu- 

 sion is so great that all power of stimulation is lost. 



It diay well be that a light breeze will serve to so strengthen the 

 odor bej'ond this point so that the power of stimulation will extend 

 beyond its normal radius. In the opposite direction the distance of 

 possible stimulation would be decreased or reduced to nothing. Yet, 

 in this case the wind serves rather to increase the distance to which 

 an already active factor is at work in a certain direction than to act 

 as a factor itself, unless it be that it exerts a stereotropic influence. 



Another point still further complicates the discussion. Flies have 

 been repeatedly referred to in literature as seeking "shelter." Cer- 

 tain it is that when meteorological conditions are unfavorable they 

 are little in evidence. This suggests that if the wind be too strong 

 flies may seek protection. 



Although the data of the present investigations indicate that wind, 

 as a seasonal factor, may have had little significance, it is by no means 

 proved that this would be so under all conditions. Munson (1901),^ 

 concerning the typhoid epidemics of 1898, says that "when a strong 

 wind constantly blows from the same direction, a fly-borne infection 

 will extend down the wind." 



Rain. — Flies are not active during inclement weather, hence dis- 

 persion is temporarily affected because of lessened activity. 



Temperature. — The same consideration applies to low tempera- 

 tures. Optimum temperatures, on the other hand, increase activity, 



