SEC. 2. SMELL. 



Odorous particles present in the inspired air passing through 

 the lower nasal chambers diffuse into the upper nasal chambers, 

 and falling on the olfactory epithelium produce sensory impulses 

 which, ascending to the brain, give rise to sensations of smell. We 

 may presume that the sensory impulses are originated by the con- 

 tact of the odorous particles with the peculiar rod-shaped olfactory 7 

 cells described by Max Schultze ; but we are as much in the dark 

 about this matter as about the development of visual sensory im- 

 pulses in the rods and cones or of auditory sensory impulses in the 

 organ of Corti. 



The subsidiary apparatus of smell is exceedingly meagre. By 

 the forced nasal inspiration, called sniffing, we draw air so forcibly 

 through the nostrils that currents pass up into the upper as well as 

 the lower nasal chambers ; and thus a more complete contact of the 

 odorous particles with the olfactory membrane than that supplied 

 by mere diffusion is provided for. 



We have every reason to think that any stimulus applied to the 

 olfactory nerve will produce the sensation of smell ; but the proof 

 of this is not so clear as in the case of the optic and auditory 

 nerves. We are, however, subject to sensations of smell not caused 

 by objective odours. The olfactory membrane is the only part of 

 the body in which odours as such can give rise to any sensations ; 



