Reactions of the Pomace Fly to Odorous Substances 517 



had been supplied with distilled water but had been kept from 

 food for twenty-four hours. If they are kept without food much 

 longer than this, they begin to die and few survive sixty hours. 

 After the flies had been allowed twenty-four hours in which to 

 enter the traps, the experiment was discontinued and the indi- 

 viduals in each trap were counted. In this way some idea of the 

 influence of different substances on the movements of the flies 

 could be ascertained. 



These experiments were preliminary, in that they aimed only to 

 determine what substances called forth positive reactions. The 



^ 



Fig. I Vial arranged as a trap. 



results, which are necessarily fragmentary, because of the difficulty 

 of dealing with odors in a quantitative way, are given in Table I. 

 From Table I it is apparent that of the ten substances which 

 were tested singly in aqueous solutions, the flies gave definite 

 positive reactions to four, namely amyl, and especially ethyl 

 alcohol, acetic and lactic acid (Experiments i, 2, 3, 5, 6). The 

 remaining substances to which the flies did not react positively or 

 did not react in numbers large enough to be significant, are propyl 

 alcohol, butyric acid, valerianic acid, glucose, amyl valerianate 

 and acetic ether. Experiments which were undertaken subse- 



