PHYSIOLOGY OF OLFACTION 47 



fairly well established that the current of air that sweeps 

 through the nasal cavity in quiet respiration is limited 

 chiefly to the non-olfactory portion of that cavity. Ac- 

 cording to Paulsen and to Zwaardemaker this current 

 even in its eddying effect does not rise above the lower 

 edge of the middle concha or at most, according to 

 Franke, the lower edge of the superior concha. This 

 limitation is probably more pronounced in expiration 

 than in inspiration. 



Although the experimental evidence does not show that 

 the respiratory current spreads to the olfactory surface 

 of the nose, odorous particles must in some way reach this 

 situation. Zwaardemaker (1895) was led to believe that 

 the diffusion of these particles played an important part 

 in this process, but diffusion is a relatively slow operation 

 and it is very doubtful if it is a significant factor in carry- 

 ing the odorous material to the olfactory receptor. It 

 seems more probable that the shifting pressures that 

 accompany respiration and the slight eddies that are 

 formed in the general current are responsible for a grad- 

 ual change of air in the olfactory cleft. The change thus 

 produced is probably too slight to be detected easily by 

 the means heretofore employed in tracing the current and 

 yet it may be sufficient to initiate such olf action as occurs 

 in quiet respiration. Olfaction thus once begun would 

 naturally excite sniffing and this process seems to be 

 entirely sufficient to account for a rapid change of air in 

 the olfactory cleft whereby olf action would be brought to 

 full height. Thus air currents are certainly the chief if 

 not the sole factors concerned with transporting the 

 odorous particles to the olfactory membranes. 



The accumulation of odorous materials on the olfac- 



