ELECTROPHYSIOLOGICAL INVESTIGATION 



95 



low but effective concentration, used briefly after a strong stimulus, either 

 failed completely or elicited weaker responses than before strong stimulus 

 appHcation. A reference stimulus is again as potent only after 5-10 min 

 of recovery are allowed. During the application of highly concentrated 

 stimuli, very often the EAG plateau is unsteady. This may also be partially 

 the result of an interaction between degree of stimulation and rate of adap- 

 tation. 



w- 



10- 



10 



10 



t^g 



Fig, 7. The stimulus-response curve of Bombyx males to ascending and descend- 

 ing concentrations of hexadeca-10-m, 12-/m/?^-dien-ol-(l). Ordinate : EAG- 

 Amplitude (from Block, Boeckh and Schneider, unpublished). 



The threshold differences between Bombykol and its isomers are 

 extremely interesting. The architecture of the molecule (Fig. 8) is obviously 

 of decisive importance for olfactory stimulation. When we checked the 

 isomers electrophysiologically, we usually found that the threshold dif- 

 ference between the " true " lure alcohol and the isomers was smaller than 

 expected from the results of behaviour tests. 



Except for a few cases where one of the isomers (mostly the \0-cis, \2-cis- 

 substance) was apparently more potent than Bombykol (Fig. 6), the isomers 

 stayed behind the Bombykol response. In some tests the curves of at least 

 three of the four isomers of the hexadecadienol met in the higher concen- 

 tration range. 



All these variations are partially the results of too few data. Since the 

 experiments are still in progress, more conclusive results are anticipated. 



