Chemoreception 



467 



of any other property thermodynamically related to the boiHng point. Simi- 

 lar studies indicate that a consistent difference exists between normal and 

 iso compounds, the normal compound being more effective; that ketones 

 stimulate more readily than phenol esters and alcohols;" that esters are more 

 stimulating than their alcohols;^^ and that increasing the chain length of 

 homologous series of alcohols or esters results in increased stimulative effect- 

 iveness. •'•' These results are essentially in agreement vi'ith the correlation 

 between boiling point and stimulating effectiveness. 



Gustation. In general, it is known that stimulation of the chcmoreceptors 

 which mediate taste in man and regulate feeding and oviposition in other 

 animals requires the contact of the stimulating substance with the sense or- 

 gan in question. Just what happens after this contact has been established 

 is not known, and indeed, among the insects it is not clear what the sense 

 organs are or precisely where they are located. It has been suggested-" that 

 the penetration of the stimulating substances into the sense cells or their ad- 

 sorption on the cell membranes is an important event in stimulation, and 

 considerable data are in agreement with this suggestion. However, grant- 



rrHVL ACETATE 



isonorvL ai.cdhol 



UOPKOfVL ACrTATt O 



o 



ETHYL monONATE 



•UTYL ALCOHOL 



BUTYL VALERATt 

 rSOAMYL VALERATE Q 



£ 



•UTYL ACETATE 



ISOAUVL ACETATE O 



HOPYL BUTYRATE 

 PROfYL VALERATE O 

 BUT-lfL BtlTYRATE 

 IIOAMYL BUTYRATE O 



OPTIMUM CONCENTRATION- '/• 



Fi^. 152. The relation between boiling point and the most attractive concentration 

 (indicated by the number of houseflics caught) of a variety of paraffin compounds. 

 After Cook," from Dethicr.''* 



ing the adsorption or penetration ot the stimulating agent, there is as yet no 

 knowledge of the events leading to the initiation of the nerve impulses. 

 Consequently, a comprehensix'c theory which is in accord with all the known 

 tacts of chemoreceptor stimulation is xet lacking. 



I he role of chemical structure in stimulation of the gustatory sense or- 

 gans has received considerable attention. Von Frisch, as a result of his sugar- 

 feeding experiments with bees, concluded that the factors involved in stimu- 



