134 Notes on Chemotrqpism in the House- Fly 



aggravated where the methyl group is augmented by union with 

 (CR 2 ) X . 



3. Compounds containing the benzene ring are unattractive though 

 not necessarily negative. These are unsaturated. 



4. Amyl compounds are probably increasingly attractive in the 

 order in which they are formed during fermentation and decomposition. 



5. If, in this series, valerianic aldehyde is less attractive than amyl 

 acetate or amyl alcohol, then it is probable that the aldehyde group, in 

 all compounds containing it, is to a certain extent negatively chemo- 

 tropic. 



There is evidently no relation between volatility and chemotropic 

 action. 



Note was made of the rates of evaporation during the experiments, 

 and these are given below, the substances being arranged in order of 

 assumed attractive power. 



It is sufficient at this stage to point out that saturated compounds 

 contained in fermenting vegetable substances and containing the mole- 

 cular group CH 3 (GH. 2 ) X may constitute the source by which the house-fly 

 is guided to its food. 



SECTION III. 



ESSENTIAL OILS. 



The experiments in this section were carried out under the same 

 conditions as those in the last. 



To give an idea of the number of house-flies caught by the traps in 

 their respective positions, a control record was taken with a known 

 quantity of grape juice. The results were as follows: 



