PHYSIOLOGY OF OLFACTION 85 



of double stimulation that has been much studied. Val- 

 entin observed that when ether and balsam of Peru were 

 smelled at the same time one by one nostril and the other 

 by the other nostril, the odors are perceived not together 

 but alternately and Valentin believed that there was 

 a sensory conflict here as in vision, when one eye is 

 directed to a field of one color and the other eye to one 

 of another color. Aronsohn (1886) noted a similar con- 

 flict between the smell of camphor and that of oil of 

 lemon. He also discovered that under similar circum- 



Table VI. 

 Pairs of neutralizing odors (Zwaardemaker, 1895, p. 168). 



Pairs of odorous bodies Neutralizing Strength 



in olfacties 



Cedarwood and rubber 2.75 : 14 



Benzoin and rubber 3.5 : 10 



Paraffin and rubber 8.5 : 14 



Rubber and wux 14 :28 



Rubber and balsam of Tolu 14 :70 



Wax and balsam of Tolu 40 :90 



Paraffin and wax 10 :20 



stances one smell could overcome another. Thus the 

 smell of camphor was neutralized by the smell of pe- 

 troleum, cologne water, oil of juniper and so forth. 

 This question was investigated much more fully by 

 Zwaardemaker (1895) who employed for this purpose 

 his double olfactometor. By this means it was compara- 

 tively easy to- balance odors and then lead one into one 

 nasal cavity and the other into the other cavity. In this 

 way complete neutralization could be attained with great 

 accuracy. Table VI gives a list of neutralizing pairs of 

 odors and the intensity in olfacties at which Zwaarde- 

 maker found neutralization to occur. 



