498 THE SENSE OF SMELL. 



odors most plainly perceived by an herbivorous animal and 

 by a carnivorous animal are different. The carnivora have 

 the power of detecting most accurately by the smell the special 

 peculiarities of animal matters, and of tracking other animals 

 by the scent ; but have apparently very little sensibility to the 

 odors of plants and flowers. Herbivorous animals are pecu- 

 liarly sensitive to the latter, and have a narrower sensibility 

 to animal odors, especially to such as proceed from other in- 

 dividuals than their own species. Man is far inferior to many 

 animals of both classes in respect of the acuteness of smell ; 

 but his sphere of susceptibility to various odors is more uni- 

 form and extended. The cause of this difference lies probably 

 in the endowments of the cerebral parts of the olfactory ap- 

 paratus. 



Opposed to the sensation of an agreeable odor, is that of a 

 disagreeable or disgusting odor, which corresponds to the sen- 

 sations of pain, dazzling and disharmony of colors, and disso- 

 nance in the other senses. The cause of this difference in the 

 effect of different odors is unknown ; but this much is certain, 

 that odors are pleasant or offensive in a relative sense only, 

 for many animals pass their existence in the midst of odors 

 which to us are highly disagreeable. A great difference in 

 this respect is, indeed, observed amongst men : many odors, 

 generally thought agreeable, are to some persons intolerable ; 

 and different persons describe differently the sensations that 

 they severally derive from the same odorous substances. There 

 seems also to be in some persons an insensibility to certain 

 odors, comparable with that of the eye to certain colors ; and 

 among different persons, as great a difference in the acuteuess 

 of the sense of smell as among others in the acuteness of sight. 

 We have no exact proof that a relation of harmony and dis- 

 harmony exists between odors as between colors and sounds ; 

 though it is probable that such is the case, since it certainly is 

 so with regard to the sense of taste ; and since such a relation 

 would account in some measure for the- different degrees of per- 

 ceptive power in different persons ; for as some have no ear for 

 music (as it is said) so others have no clear appreciation of the 

 relation of odors, and therefore little pleasure in them. 



The sensations of the olfactory nerves, independent of the 

 external application of odorous substances, have hitherto been 

 little studied. It has been found that solutions of inodorous 

 substances, such as salts, excite no sensation of odor when in- 

 jected into the nostrils. The friction of the electric machine 

 is, however, known to produce a smell like that of phosphorus. 

 Hitter, too, has observed, that when galvanism is applied to 

 the organ of smell, besides the impulse to sneeze, and the tick- 



