ON SMELL. 
283 
power of registering, not the number of vibrations per second^ as 
our optic nerve does, but the amplitude of the vibration ; that 
difference w^hich we should express, if we were talking of light, 
.as a dim light, or a bright light. 
We thus see that four of the six senses are probably affected 
by vibration. 
It is not my intention to speculate on the nature of taste, 
but to consider what arguments can he adduced to shew that the 
sense of smell is also caused by vibrations ; what the nature of 
these vibrations, if they exist, is ; and what is their probable 
number per second. 
The sense of smell is caused by the contact of certain 
substances with the terminal organ of the olfactory nerves, w^hich 
are spread as a network over a mucous membrane, lining the 
upper part of the nasal cavity. Each nerve consists of a number 
of small bundles, themselves capable of being split into extremely 
fine nerve fibres. There are spindle-shaped cells connected with 
these nerves, from which proceed two processes, one to the 
surface, provided with bundles of long haiiiets, the other passes 
to the interior. It is these hairlets which are probably the 
proximate cause of smell. 
Let us consider, first, by wLat are smells excited? The 
operation of smelling is performed by sniffing, that is, by a 
series of short inhalations of air bearing with it the odorous 
body. The first question which suggests itself is, is the sub- 
stance which excites sensation a liquid, solid, or gas ? It has 
been tried, by Weber, to fill the nose with Eau de Cologne and 
water, lying on the hack for that purpose, and pouring the 
liquid into the nostrils by a funnel. No sensation is produced, 
I have myself tried the experiment, and can confirm his 
observation. There is an irritating feeling, but no smell. Of 
course, on washing out the nose, or blowing it, the characteristic 
smell is at once noticeable. 
