E. R. Speyer 133 



Experiment 9. 



Date:— October 7th-9th. 



General weather conditions: — Warm, dull. 



Duration of experiment : — 45 hours. 



Flies caught 



Substance Amount , >- s 



c.c. <y ? Total 



Valerianic aldehyde 20 3 6 9 



Benzaldehyde 40 3 3 



Cinnamaldehyde 40 1 1 



Experiments with oil of bitter almonds point to the fact that benz- 

 aldehyde is not positively chemotropic, and the same applies to cinnam- 

 aldehyde. 



Experiment 10. Acids. 



Date:— October 6th-9th. 



General weather conditions: — Warm, dull. 



Duration of experiment: — 69 hours. 



Flies caught 



Substance Amount „ *- „ Percentage 



c.c. S ? Total 



Valerianic acid 20 17 28 45 71 



Benzoic acid in 100 % ethyl alcohol 45 9 7 10 26 



Cinnamic acid in 100 % ethyl alcohol 70 1 1 2 3 



100 



The last figures are more satisfactory, and give valerianic acid a 

 percentage close to that of Exp. 7 when this liquid was used in company 

 with an alcohol and an acetate. From observations made upon solid 

 benzoic and cinnamic acids it is probable that these substances owed 

 their attractive features solely to the ethyl alcohol in which they were 

 dissolved, and benzoic acid may actually be negatively chemotropic. 



A curious observation was made upon flies exposed to cinnamic acid, 

 in that they show a prolonged immunity to the fumes of hydrocyanic 

 acid gas. The effect of cinnamic acid is therefore probably antidotal to 

 the insects. 



The conclusions to be drawn are as follows : 



1. Saturated alcohols, aldehydes and acids are positively chemo- 

 tropic in products of fermentation, as far as amyl compounds are con- 

 cerned. 



2. Alcohols, aldehydes and acids containing the methyl group CH 3 

 are positively chemotropic, except in cases where their molecular weight 

 is about 30 (methyl alcohol) or below, the chemotropic stimulus being 



9—3 



