lfactory nerves are more stimulated, and produce a stronger
sensation.

In order that this sense may be enjoyed in perfection, it is
necessary that the organ of smell be in a proper state or condition
to receive impressions, and that the odorous bodies be likewise in a
proper state. With respect to the first, it is necessary that the
state of the nerves be sound, and particularly that they be kept in a
proper state with respect to moisture.

With regard to the odorous bodies, it is necessary, first, that their
minute particles should be disengaged, either by heat, friction,
fermentation, or other means capable of decomposing those bodies
which are the subjects of smell: secondly, that they may be capable
of assuming the vaporous or gaseous state, by combining with caloric,
or at any rate, that they should remain for a certain time dissolved
or suspended in the air: thirdly, that they should not meet with any
substance in their way to the nostrils, which is capable of
neutralising them, or altering their properties by its chemical
action.

Notwithstanding all the pains which physiologists have taken to
detect the nature of odorous bodies, they have met with but little
success. They are so extremely minute as to escape the other senses,
and we can only say that they must be composed of particles in an
extreme state of division and subtilty, because very small quantities
of odorous matter exhale a sufficient quantity of particles to fill a
large space. A grain of camphor, musk, or amber exhales an odour
which penetrates every part of a large apartment, and which remains
for a long time.

There is perhaps no substance in nature which is absolutely incapable
of being changed from a solid state into that of a fluid or gas, by
combining with caloric; though different substances require very
different quantities of heat to produce those effects. Those which
are with difficulty converted into fluids or gases, are termed fixed,
while those which are easily changed are called volatile; though
these are only terms of comparison, for there is probably no body
which is absolutely fixed, or incapable of being reduced to vapour by
the application of a sufficient degree of heat.

The odorous property is probably as general as that of being
convertible into gas. There is perhaps no body so hard, compact, and
apparently inodorous, as to be absolutely incapable of exciting smell
by proper methods: two pieces of flint rubbed together