526 



Willi a 7n Morton Barroius 



which had been added 8 per cent of acetic ether. Of the dilutions 

 used, 125 per cent of the mixture induced the largest number of 

 flies to react positively. It is probable that the experiments were 

 complicated by the presence of a higher per cent of acetic ether 

 than is met with under natural conditions. In Table I, Experi- 

 ment 3, about .04 per cent of acetic ether was added, respectively, 

 to 10 per cent alcohol and to 4 per cent acetic acid, and in both 

 instances there was an immense increase in the number of re- 

 sponses as compared with the responses to those reagents alone; 

 this increase must have been due to the slight amount of acetic 

 ether present. We may safely conclude that acetic ether probably 

 plays some part in the reactions of Drosophila to normal food. 



TABLE VI 



The riufiibers of fiies which reacted positively to each of three di^erent strengths of the mixture of alcohol, 

 acetic acid and acetic ether. In each experiment the number of flies used was one hundred 



The foregoing experiments show that Drosophila is positively 

 chemotropic to alcohol, acetic acid and under certain conditions 

 to acetic ether. The optimum strengths of alcohol and of acetic 

 acid are 20 and 5 per cent, respectively, while that of acetic ether 

 is uncertain, but must be only a fraction of i per cent. 



Table VII, made up from data given by Leach ('05), shows that 

 alcohol and acetic acid are commonly found in cider vinegar, 

 fermented cider, and California sherry in per cents that are close 

 to those which call forth the largest numbers of reactions in Droso- 

 phila. 



Acetic ether is found in these fluids in very slight traces. 



