SENSE OF SMELL. 239 



quantity oT air for several years ( 104, note) ; and there are some volatile 

 fluids, such as water, which are entirely inodorous. The Schneiderian or 

 Pituitary membrane is the seat of the sense of smell ; but it is probable that 

 every part of it is not equally endowed with the faculty of distinguishing 

 odours, which is a very different power from that of becoming sensible of irri- 

 tation from them. The Olfactory nerves cannot be traced to the membrane 

 covering the middle and inferior spongy bones, or to that which lines the dif- 

 ferent sinuses, these parts of the surface being supplied by the fifth pair only ; 

 and it is a matter of common experience, that we cannot distinguish faint 

 odours, unless, by a peculiar inspiratory effort, we draw the air changed with 

 them to the upper part of the nose. In animals living in the air, it is a neces- 

 sary condition of the exercise of the sense of Smell, that the odorous matter 

 should be transmitted by a respiratory current through the nostrils ; and that 

 the membrane lining these should be in a moist state. Hence, by breathing 

 through the mouth, we may avoid being affected by odours, even of the 

 strongest and most disagreeable kind ; and in the first stage of a catarrh, 

 when the ordinary mucous secretion is suspended, the sense of smell is blunted 

 from this cause, as it afterwards is from the excess in the quantity of the fluid, 

 which prevents the odoriferous effluvia from coming into immediate relation 

 with the sensory extremities of the nerves. Hence we may easily compre- 

 hend, that section of the fifth pair, which exercises a considerable control over 

 the secretions, will greatly diminish the acuteness of the smell ; and it will 

 have the further effect of preventing the reception of any impressions of irri- 

 tation from acrid vapours, which are entirely different in their character from 

 true odorous impressions, and which are not transmitted through the olfactory 

 nerve ( 220). The nasal' passages may indeed be considered as nerving, in 

 the air-breathing Vertebrata, two distinct offices ; jhey constitute the organ of 

 smell, through the distribution of the olfactory nerve upon a part of their sur- 

 face ; but they also constitute the portals of the respiratory organs, having for 

 their office to take cognizance of the aeriform matter which enters them, and 

 to give warning of that which would be injurious; this latter function is per- 

 formed by the Fifth pair, as by the Par Vagum in the glottis. It is through 

 this nerve, that the act of sneezing is excitable : the evident purpose of which 

 is the ejection of a strong blast of air through the nasal passages, in such a 

 manner as to drive out any offending matter they may contain. 



325. The importance of the sense of Smell among many of the lower ani- 

 mals, in guiding them to their food, or in giving them warning of danger, and 

 also in exciting the sexual feelings is well known. To Man its utility is very 

 subordinate under ordinary circumstances ; but it may be greatly increased 

 when other senses are deficient. Thus, in the well-known case of James 

 Mitchell, who was deaf, blind and: dumb, from his birth, it was the principal 

 means of distinguishing persons, and enabled him at once to perceive the en- 

 trance of a stranger. It is recorded that a blind gentleman, who had an anti- 

 pathy to cats, was possessed of a sensibility so acute in this respect, that he 

 perceived the proximity of one that had been accidentally shut up in a closet ' 

 adjoining his room. Among Savage tribes, whose senses are more cultivated 

 than those of civilized nations, more direct use being made of the powers of 

 observation, the scent is almost as acute as in the lower Mammalia; it is as- 

 serted by Humboldt, that the Peruvian Indians in the middle of the night can 

 thus distinguish the different races, whether European, American Indian, or 

 Negro.* The agreeable or disagreeable character assigned to particular 



* The author has been assured by a competent witness, that a lad in a state of som- 

 nambulism had his sense of Smell so remarkably heightened, as to be able to assign 

 (without the least hesitation) a glove placed in his hand~to its right owner, in the midst 

 of about thirty persons, the boy himself being blindfolded. 



