522 



William Morton Barrows 



marks the edge of the current of ammonium chloride, which shows 

 that none of the ammonia moved against the current toward E. 

 In using the apparatus it was so placed that the flies, which are 

 positively phototropic, would creep under the influence of light 

 from chamber E to chamber G. A number of hungry flies were 

 placed in chamber E\ the current of air was then started; and the 

 two vials were placed in position, one containing the substance to 



TABLE II 



The numbers of fiies which reacted positively to each of eight di^erent strengths of ethyl alcohol. In each 

 experiment the number of flies used was one hundred 



Number of the 

 experiment 



15- 



ICX) 



75 

 5° 

 25 

 25 

 20 



IS 

 IS 



Number of flies that 

 entered the 



Alcohol 

 trap 



Control 

 trap 



Number of flies that 

 turned toward but 

 did not enter the 



Control 

 trap 



Alcohol 

 trap 



s « fc 



2 S "o 



7-S 



3 

 i-S 



I -75 



be tested, the other containing water used as a control. The slide 

 was then opened far enough to allow a few flies at a time to pass 

 down the trough toward the light. The flies, that reacted posi- 

 tively by turning abruptly toward the traps, were counted as were 

 those that entered either of the traps. After fifty flies had been 

 admitted to the trough, the slide was closed and the traps were 

 interchanged. Now fifty more flies were allowed to pass through 



