SMELL—HEARING. 71 
on the tongue both simple and compound papille, the former very much 
like those in the skin, the latter of various forms. The sense of taste is 
very much assisted by that of Smell, as is seen in the case of aromatic 
substances, the taste of which is much weaker when the nostrils are 
closed than when they are open. Other substances, called pungent, such 
as pepper, mustard, &c., when tasted, produce a sharp, pricking sort of 
sensation, which is also produced on the skin—that is, by the sense of 
touch—if the same substances be applied to it strongly enough. Touch 
and taste are thus very closely connected. It may be remarked that the 
sense of true touch is very acute on the tip of the tongue. 
It is always necessary that the tongue be’ moist in order to taste 
anything ; and it seems, too, to be a condition in substances having taste 
that they be soluble in water, as bodies that cannot be dissolved in water 
are quite tasteless. 
Smell. 
The seat of the sense of smell is in the cavities of the nose into which 
the nostrils open, and which open behind into the pharynx, or entrance to 
the windpipe, above the soft palate. The two cavities are separated from 
each other by a vertical partition, principally composed of cartilage, of 
which, indeed, the greater part of the framework of the nose is composed. 
The walls of these cavities are lined with a thick, velvety membrane, 
over which the olfactory nerves are distributed. It will be remembered 
that the outer walls are partly formed by the ‘turbinated’ bones (p. 45), 
which form three projections on each side, with hollows between. The 
object of this arrangement is to increase the surface over which the 
membrane is spread, as it is on this to a great extent that the acute- 
ness of the sense depends. The membrane is kept continually moist by 
mucus, to which the particles of any substance smelt attach themselves 
when carried into the nostrils by the air, and thus, coming in contact 
with the extremities of the olfactory nerves, produce the impression 
which gives rise to the sensation of smell. It is on the roof of the 
cavity that the sense is most acute; and the effect of snuffing up the 
air is to throw the particles on that part, so as to enable us to detect 
odours that might otherwise escape us; although most people are 
unconscious of the object of this action. 
Hearing. 
The ear, the organ of hearing, is more complicated than any of the 
organs of the senses yet described. It consists of three parts—the external, 
middle, and internal ears, the last two lying in cavities in the temporal 
bones. The external ear consists of the fleshy part seen on each side of 
