58 SUPPLEMENT ON 



" Necessarily transmitted by the air, which is their only 

 vehicle, odours have a tendency to penetrate along with it 

 into the body of the animal ; arrested in their passage in a 

 sort of custom-house, (bureau de douane,) where they are 

 to be promptly visited and analyzed, they are put in contact 

 with a humid surface, with which they have some affinity. 

 They immediately combine with it ; but at the same time 

 they touch, and give notice of their presence to the nerves 

 distributed over these same parts which report to the brain, 

 of which they are the elongation, the chemical or physical 

 action, in a word, the sort of sensation which they denote, or 

 which perhaps they have experienced," 



" Smells, therefore, like all other physical sensations, are a 

 sort of touch in which the body, whatever be its nature, comes 

 to the organ, and transports itself on the only part of the 

 animal where its action can manifest all its properties. In 

 the final analysis, all our sensations are thus reducible, either 

 to a passive taction, i. e. to the action of being touched, or 

 to an active tact, which gives us the faculty of carrying our 

 bodies or some parts thereof to the surface of objects, for the 

 purpose of ascertaining their qualities." 



" By this admirable arrangement we experience the action 

 of the majority of bodies. It is thus that light, an impon- 

 derable fluid, which is so variously modified on the surface 

 of objects, transmits their image into the eye by being ap- 

 plied exactly on the nerve of the retina ; that the matter of 

 heat or caloric, is placed in equilibrium with our bodies, 

 is applied to, or withdrawn from them, thus manifesting its 

 presence or absence ; that the vibrations communicated to 

 bodies are transmitted either directly by contact, or by the 

 intervention of air or gases, to a small quantity of air con- 

 tained in one of our organs, with which they unite in perfect 

 harmony to enable us to appreciate sounds and produce hear- 

 ing; that, in fine, the substances which are susceptible of 



