E. R. Speyer 



127 



that, during the first 24 hours, while no controls were used, the figures 

 for the experiment substances were vanilla extract 25, lemon extract 12, 

 spirit of vinegar 3. 



It may be well here to give the results of these two experiments in 

 percentages, to give an idea of the proportion of flies out of 100 which 

 would enter each trap. 



100 



100 



The figures for the controls are, of course, derived by calculation, 

 allowance being made for the three traps instead of one in each case, 

 and for the duration of time in the second case. In both cases the 

 position of vanilla extract appears to be approximately the same, 

 showing that the figures are reliable. 



It may be added that the number of flies caught in the weak controls 

 in Exp. 1 are in a rough direct proportion to their experiment substances, 

 so that it would appear that they had, themselves, a definite attraction 

 to the flies brought into their proximity by the strongly attractive 

 agents, and doubtless had the effect of compensating for the error due 

 to flies leaving an experiment substance and flying to another. 



Experiment 3. The increase in attraction of banana due to fermentation 



and decomposition. 



Date : — August 2Sth-September 2nd. 



General weather conditions: — Du'l and cool during first period. 



Hot and bright after. 

 Total duration of experiment: — 138 hours. 



By an unfortunate oversight, the numbers of flies found dead, and of those found 

 alive in the trap were not differentiated during Period 3. 



The positively chemotropic stimulus in banana and in grape juice is 

 due to products of fermentation. To prove this beyond doubt a fresh 



