PHYSIOLOGY OF OLFACTION 57 



tion is accomplished through very small, often infinitesi- 

 mally small, amounts of material, and yet these amounts 

 involve immensely large numbers of molecules of the 

 odorous substance. 



4. Physical Condition of Stimulus, Gas or Solution? 

 In olf action in the air-inhabiting vertebrates the stimu- 

 lus has been generally assumed to be material particles 

 in a vaporous or gaseous condition and not, for instance, 

 in the form of a solution. 



This opinion was long ago supported by the experi- 

 ments of Tourtual (1827) and especially of Weber (1847) 

 both of whom believed that it could be shown that sub- 

 stances that could be smelled as vapors could not be 

 smelled as solutions when introduced as such into the nose. 

 Thus Weber was unable to recognize cologne water when 

 this liquid, much diluted with ordinary water, was poured 

 into his nasal cavities. He, therefore, concluded that 

 though the vapor from cologne water was easily smelled, 

 a solution of it was not so sensed and that hence the 

 vaporous state of the substance was necessary as a stim- 

 ulus for the olfactory organ. This conclusion was ac- 

 cepted by a number of investigators including Nagel 

 (1894, 1904), Zwaardemaker (1895), Haycraft (1900) 

 and others. 



Aronsohn, in 1884, pointed out the great influence 

 that water and temperature had on the olfactory organ. 

 Ordinary cold water when introduced into the nose will 

 so affect the organ of smell that olfaction is impossible 

 for some time to come. Cold water is known to excite 

 an increased production of mucous whose volume would 

 materially interfere with stimulation by covering up the 

 olfactory surfaces. Moreover if the action of water on 



