136 THE PHYSIOLOGY OF INSECT SENSES 



Further analyses of the date of Dethier and Chadwick (1948 b, 1950) 

 suggest that the important factor in stimulation by non-electrolytes 

 is adsorption (Davies and Taylor, 1959). When the logarithm of rejec- 

 tion thresholds (molar concentration) is plotted against the logarithm 



1.0 



0.0 - 



I— 



Ul 



o 

 a: 



o 

 to 



>- 



CD 



O 

 UJ 



O 



UJ 



o 



o 

 o 



q: 

 < 



_j 

 o 



o 

 o 



-1.0 



-2.0 



-3.0 



-4.0 



O ALDEHYDES 

 A KETONES 



NORMAL ALCOHOLS 



• SECONDARY ALCOHOLS 



0.0 



0.4 0.8 



LOG NUMBER OF ATOMS 



12 



Fig. 80. Rejection of aldehydes, ketones, and secondary alcohols by 

 Phormia. (From Chadwick and Dethier, 1949.) 



of the adsorption constant for an oil/water interface the slope of the 

 resulting line is very near that expected for adsorption from solution 

 on to a pure lipid membrane. 



Rejection Thresholds - Organic Electrolytes 



The situation with regard to organic electrolytes is less clear than that 

 for the non-electrolytes. Tests with a number of fatty acids indicated 

 that while the H ion is the principal factor in stimulation with com- 



