STRUCTURE OF SENSIFEROUS ORGANS 299 



are caused by odorous bodies; and we may pass 

 on to the next step of the inquiry namely, how 

 the odorous body produces the effect attributed 

 to it. 



The first point to be noted here is another fact 

 revealed by experience; that the appearance of 

 the sensation is governed, not only by the 

 presence of the odorous substance, but by the 

 condition of a certain part of our corporeal struc- 

 ture, the nose. If the nostrils are closed, the 

 presence of the odorous substance does not give 

 rise to the sensation; while, when they are open, 

 the sensation is intensified by the approximation 

 of the odorous substance to them, and by snuffing 

 up the adjacent air in such a manner as to draw 

 it into the nose. On the other hand, looking at 

 an odorous substance, or rubbing it on the skin, or 

 holding it to the ear, does not awaken the sensa- 

 tion. Thus, it can be readily established by 

 experiment that the perviousness of the nasal 

 passages is, in some way, essential to the sensory 

 function; in fact, that the organ of that function 

 is lodged somewhere in the nasal passages. And, 

 since odorous bodies give rise to their effects at 

 considerable distances, the suggestion is obvious 

 that something must pass from them into the 

 sense organ. What is this " something," which 

 plays the part of an intermediary between the 

 odorous body and the sensory organ? 



The oldest speculation about the matter dates 



