.THE SENSE OF SMELL. 287 



miptnkeu for real seusntious of smell. Now, as odorous substances can produce 

 sensations of sracU only wlveu in contact with the upper parts of the i^asal 

 cavity, the motion of the odorous air caused by the nasal inhalation seems to 

 have no other aim but to make it stream towards the upper smelling regions of 

 the cuticle ; and it would not appear irrational to suppose that when the air 

 is in rest in the nasal cavity there arises no smell from the odorous atmosphere, 

 because the gradual blending of the external with the internal air, in 

 consequence of so-called diffusion, would not be sufficient to convey an 

 adequate quantity of the odorous substance to the upper parts of the cuticle. 

 But besides its being evident that after a sufficient lapse of time that blending 

 must in all cases become so complete as to equalize the amount of odorous sub- 

 stance in the nose with that in the external air, the Insufficiency of that expla- 

 nation can also be proved by a direct experiment. If we blow some odorous 

 air directly against the upper parts of the nose outside by means of a small 

 tube introduced into the nasal cavity, there arises no sensation of smell, or at 

 least a considerably fainter one than when drawing the same air through the 

 nose by a motion of breathing. This shows that the motion of the odorous air 

 which is caused by inhalation must have in it something peculiar, and that this 

 peculiarity is the conditional something for the atfection of the nerve of smell. 

 But in what this peculiarity consists is another enigma for the solution of which 

 physiology as yet offers but a sugg-estioa itself iji need of a farther explanation. 

 The lower nasal shell, which by itself is no medium for sensations of smell, 

 seems yet to bear a relation to the odorous air entering from without, which is 

 important for the development of a sensation of smell. It has been observed that 

 the loss of the projection of the nasal partition, caused by disease, for instance, 

 is generally connected with a considerable lessening or with an entire loss of 

 the sense of smell, though it must be remarked that in these observations it 

 may hardly have been ascertained whether the upper nasal shell had not under- 

 gone simultaneously with the lower such alterations as would directly cause 

 the loss or a weakening of that sense. The part to be played by the lower 

 nasal shell can only be a subject of conjecture. To these v/e are led by an 

 examination of the position and form of the lower shell. This (as shown also - 

 in the above figure) forms a ledge extending from front to rear in a crooked 

 oblique direction, and having its concave plane turned towards the bottom of 

 the nasal cavity, and its convex plane towards the upper shells, its interior list 

 being strongly bent downward. When propelling the atmospheric air into the 

 nose by an expansion of the chest, the current of air receives such a direction 

 from its position and form of the nostrils that it strikes the list of the lower 

 shell, the nostrils extending downward, so that the nasal entrance presents a 

 funnel turned upward. Were the nostrils perpendicular, and therefore the 

 nasal entrance on each side a funnel turned backward, the current of air thus 

 introduced would receive a direction rearward, streaming by the shortest possible 

 way, along the bottom of the nasal cavity, towards its rear opening toward 

 which it would be attracted, and being prevented by the gorge of the lower shell, 

 as if by an umbrella, from ascending to the smelling region. But as it is, the 

 stream of air receives an oblique direction upward, and must so strike the op- 

 posite list of the lower shell as to break on it, and thence to stream partly along 

 its under plane towards the opening, and partly along its oblique convex upper 

 plane towards the upper shell. The more effectively we iuuale by the nose, 

 the more surely and effectively the current of air is led towards the lower shell, 

 and the greater becomes the part of the current branching oft' upwards. The 

 &tre<tming of the air against the lower shell can further be promoted by changing 

 the form of the nasal entrance : the operation of snuffing, at least, seems to be ex- 

 plainable in this way. The wings of the nose are by it drawn upward so as to turn 

 the nasal hole a little rearward, in consequence of which the inhaled current 

 of air is necessarily turned still more directly upward, and a greater part of id 



