702 



SMELL. 



sence of food, to indicate its direction and 

 thus to guide the animal towards it, and to 

 aid in the discrimination of its qualities. We 

 always find the olfactive organ placed in the 

 neighbourhood of the mouth ; its connection 

 with the respiratory apparatus is by no means 

 so constant. In air-breathing vertebrata, 

 whose olfactive cavity opens into the pharynx, 

 the sense of smell largely participates in that 

 of taste (see TASTE), being the means by 

 which we take cognisance of the flavours of 

 sapid bodies introduced into the mouth. Of 

 the importance of this sense in directing ani- 

 mals to their food, it is needless to multiply 

 instances ; but we may remark that, from ob- 

 servation of the actions of the human infant, 

 we are well convinced that it is rendered 

 cognisant by smell of the neighbourhood of 

 its nurse, long before it recognises her by 

 sight, and that this sense is its guide in seek- 

 ing the source o ( its nutriment. How purely 

 instinctive this action is, that is, how com- 

 pletely independent of all experience, and en- 

 tirely dependent upon the provocative sens- 

 ation, is well shown by the experiment of 

 Galen, who placed a kid, just dropped, near 

 three vessels, one filled with milk, another 

 with hone}, and another witli wine ; after 

 smelling at all three, it presently began to 

 drink the milk. It would seem to be by the 

 information conveyed through their smell, 

 that bees are induced to fly to pastures at a 

 great distance from their hive ; and it would 

 not seem improbable that the sense of dircc- 

 lion, which is so remarkably displayed by 

 many animals, is the result of the acuteness of 

 their olfactive power. Whilst the chief use of 

 smell to the carnivorous tribes is to guide 

 them to their prey, the herbivorous races, 

 whose food is constantly within their reach, 

 are warned by its means of the neighbourhood 

 of their enemies. The sense of smell is sub- 

 servient to defence in another way; being the 

 means by which the foetid scents, emitted by 

 many animals under the influence of alarm, 

 deter their enemies from further pursuit. In 

 nearly all animals, the sexual secretions are 

 more or less odorous ; and these would seem 

 to be intended, not merely to contribute to 

 make the sexes aware of each other's prox- 

 imity, through the sense of smell, but also, in 

 many instances, to serve as a provocative to 

 sexual desire. The odours which are attrac- 

 tive to animals are usually related either to 

 their food or their sexual instinct ; but there 

 are cases in which animals seem to delight in 

 odours which have no such relation : thus, 

 cats seem to revel, as it were, in the odour of 

 Nepeta (catmint) or Valerian. 



In the air-breathing vertebrata, the sense of 

 smell is, as it were, the sentinel of the respi- 

 ratory organs, having for its office to take 

 cognisance of the aeriform fluids which enter 

 them, and to give warning of such as are in- 

 jurious. The contact of irritating matters, 

 however, is perceived (as already stated) 

 through the general sense of feeling, not the 

 special sense of smelling; and it is through 

 the fifth pair that the act of sneezing is ex- 



cited, the purpose of which is to expel such 

 particles from the nasal cavity. The distinc- 

 tion is well seen in some air-breathing inverle- 

 brata, whose organ of smell is seated in the 

 head, whilst the impression of irritants on the 

 respiratory surface, exciting reflex movements 

 for the purpose of avoiding or expelling them, 

 is made through the stigmata. Thus M. 

 Duges relates* that if the stigmata on one 

 side of a decapitated Scolopendra be exposed 

 to an irritating vapour, the body will be imme- 

 diately flexed in the opposite direction ; and 

 that if the stigmata on the opposite side be 

 then similarly irritated, a contrary movement 

 will occur ; whilst by exposing the anterior 

 stigmata on one side, and the posterior on the 

 other, to the same irritation, the body will be 

 bent into the form of the letter S. 



In man, the sense of smell is not ordinarily 

 so acute as it is in many of the lower animals ; 

 yet it is very possible that it may be capable 

 of taking cognisance of a greater variety of 

 odours. In the selection of his food, it is to 

 him by no means the infallible guide that it 

 seems to be in many other races ; for it not 

 only gives no warning, in many instances, of 

 what is noxious, but renders certain poisonous 

 substances (as, for instance, those charged 

 with prussic acid or the essential oil of al- 

 monds) positively attractive. So, again, in 

 regard to the respiratory organs, whilst it 

 gives warning of the presence of certain gases 

 and emanations which are injurious, it takes 

 no cognisance of many others which are not 

 less hurtful. In the ordinary conditions of 

 civilised life, man is not dependent upon his 

 sense of smell for many of the ends which it 

 answers in other animals ; hence this sense is 

 altogether subordinate to others, and the want 

 of it is not usually attended with any great 

 inconvenience. But the case is far different 

 among savage tribes, to whom it is as impor- 

 tant as it is to other animals in a state of 

 nature, and in whom it seems to acquire, by 

 the constant habit of attention to its indica- 

 tions, a similar acuteness. Thus, it is stated 

 by Humboldt that the Peruvian Indian, in 

 the middle of the night, is informed of the 

 proximity of another individual by his smell, 

 and can distinguish by his sme'l whether the 

 stranger be an European, an American Indian, 

 or a Negro. It has even been asserted that 

 some other savage tribes of mankind are 

 enabled to follow a track by the scent of the 

 footsteps, like the bloodhound. The sense of 

 smell, moreover, usually acquires great acute- 

 ness, when, from deficiency of the other senses, 

 its indications become the chief or only means 

 of recognising bodies not in immediate con- 

 tact with the individual. Thus, in the well- 

 known case of James Mitchell, who was deaf, 

 blind, and dumb from his birth, it was the 

 principal means by which he distinguished 

 persons, and enabled him at once to perceive 

 the entrance of a stranger. Mr. Wardrop 

 gives the following curious account of the 

 mode in which he exercised this sense, and of 



* Op. cit. torn. i. p. 1C2. 



