136 Notes on Chemotropism in the House-Fly 



Here again the oils are seen to be almost totally unattractive. The 

 stray insects which enter the traps do so merely by accident. 



Eucalyptus oil is said to contain valerianic acid, and it is noteworthy 

 that no flies were attracted to it. 



It has been demonstrated that these essential oils are unattractive 

 but it still remains to be shown if any of them are actually repellent, 

 i.e. negatively chemotropic. 



For this purpose, the traps were used in the same positions as before, 

 but under each were placed two dishes — one containing a known quantity 

 of an essential oil, and the other a known quantity of grape juice. 



At the end of each period of time the traps were changed as to their 

 positions, a new supply of grape juice being used for each period, and 

 the oils being left to evaporate through the whole time. 



This was done particularly to avoid fermentation of the grape juice, 

 and total evaporation, for the amount of alcohol formed in the fer- 

 menting liquid volatilises at a high speed, leaving behind carbohydrates 

 in the form of sugar. 



Experiment 14. Repulsion by essential oils. 



Date: — September 21st-24th. 



General weather conditions : — Very hot, storms at termination. 



Total duration of experiment : — 72 hours. 



Flies caught 



It would appear that, although strongly repellent at first, these oils 

 lose their repellent properties with evaporation, and further that the 

 attractive qualities of grape juice emanate through the oils, thus ap- 

 proximating insects to the traps, into which they rush in great numbers 

 when the repellent properties disappear. 



An experiment made shortly after, substituting camphor oil for 



