CHEMORECEPTION 137 



pounds of this type, a contribution is made also by the anion or un- 

 dissociated acid, which is effective in inverse proportion to the hydro- 

 phile nature of the molecule. The relationship is thus very similar to 

 that found with the same class of compounds for human taste (cf., 

 e.g., Taylor er^/., 1930). 



i.5r*' 



Q 



_J 

 O 

 X 

 CO 

 bJ 



cr 



I 



z 

 o 



t- 

 o 



UJ 



-3 

 UJ 



on 



■z. 

 < 



Q 

 UJ 



0.75 



0.50 - 



0.25 - 



4 5 6 7 8 9 10 II 12 13 14 

 NUMBER OF C ATOMS 



Fig. 81. Relation between the stimulating efficiency of organic salts 

 and chain lengths of the anion. (From Dethier, 1956.) 



Tests with homologous organic salts show that beginning with the 

 five-carbon compound there is a logarithmic decrease similar in all 

 respects to that observed with non-polar homologues (Fig. 81) 

 (Dethier, 1956). 



Acceptance Thresholds 



Among compounds acceptable to insects carbohydrates are the most 

 usual and important. Comparisons of the acceptability of various 



