12 INNERVATION. [CHAP. XVI. 



fore be concluded, that sensations of smell are excited in it by sub- 

 stances brought to it through the water, corresponding in kind with 

 those brought in the other case through the air, but eventually dis- 

 solved in the moisture of the membrane. The nature of the sensa- 

 tion will depend on the special sensibility of the nerve, which in 

 both cases can be excited only by the stimulating substance in so- 

 lution; and whether air or water brings the stimulus to the surface 

 of the membrane, is made important only by the special adaptation 

 of that surface to the contact of one or the other medium. 



We may here notice two important reasons for the situation of 

 the organ of smell, so high up in the nose, in addition to the ob- 

 vious one of the protection from mechanical injury thus afforded to 

 so delicate a part. These are, that it is thereby screened from the 

 contact of air either too cold or too dry. The interposition between 

 the outer orifice and the organ of smell of projecting and folded 

 membranes of active secreting powers, and containing large reser- 

 voirs of blood (in the plexuses already described), seems designed 

 to answer both these purposes. These parts break the force of the 

 current, warm it, and impart that degree of moisture which is best 

 calculated to aid the solution of the odoriferous particles on the 

 sentient surface to which they are afterwards applied. The re- 

 markable complexity of the lower turbinated bones in animals with 

 acute scent, without any ascertained distribution of the olfactory 

 nerves upon them, has given countenance to the supposition that the 

 fifth iierve may possess some olfactory endowment, and seems not 

 to have been explained by those who rejected that idea. If con- 

 sidered as accessory to the perfection of the sense in the way above 

 alluded to, this striking arrangement will be found consistent with 

 the view which limits the power of smell to the first pair of nerves. 



We have already remarked that the exercise of the sense of 

 smell is not attended with more than a general idea of locality. 

 The sensation is even more simple in this respect than that of taste. 

 Unless the experiment be made, we know not that we are constantly 

 exerting the sense on two sides, for the double sensation is per- 

 ceived as a single one. Our observations on the anatomy of the olfac- 

 tory nervous apparatus may assist in the explanation of this fact. 



The sense of smell maybe voluntarily heightened by short and quick 

 inspirations, which drive the air smartly against the upper region 

 of the nose, and thus lead to the more effectual detention of its 

 odoriferous particles by the membrane, while the attention is given 

 to its sensations. On the other hand, by closing the nostrils, and 

 breathing through the mouth, all access to the organ of smell is 



