ss
occasion to exercise this sense; and the less any sense is exercised,
the less acute will it become; hence it is, that those whom necessity
does not oblige to to exercise their senses and mental faculties, and
who have nothing to do but lounge about, and consume the fruits of
the earth, become half blind, half deaf, and, in general, have great
deficiency in the sense of smell. The use of spirituous liquors, and
particularly of tobacco in the form of snuff, serves likewise in a
remarkable manner to deaden this sense.

Savages, however, who are continually obliged to exercise all their
senses, have this, as well as others, in very great perfection. Their
smell is so delicate and perfect, that it approaches to that of dogs.
Soemmering and Blumenbach indeed assert, that in Africans and
Americans the nostrils are more extended, and the cavities in the
bones lined with the olfactory membrane much larger than in
Europeans.

I have already observed the powerful effects which some odours have
upon the nervous system. There are some which agreeably excite it,
and produce a pleasant and active state of the mind, while others, on
the contrary, produce the most terrible convulsions, and even
fainting. Those particular antipathies with respect to smells, arise
sometimes from something in the original constitution of the body,
with which we are unacquainted, but generally from the senses having
been powerfully and unpleasantly affected by certain odours at an
early period of life. The latter may often be cured by resolution and
perseverance, but the former cannot.

The sense of smell sometimes becomes too acute, either from a
vitiated state of the organ itself, which is not often the case; or
from an increased sensibility or irritability of the whole nervous
system, which is observed in hysteria, phrenitis, and some fevers.

This sense is however more often found deficient; and this may arise
from a fault in the brain or nerves, which may either proceed from
external violence, or from internal causes. A defect of smell often
arises from a vitiated state of the organ itself; for instance, if
the nervous membrane is too dry, or covered with a thick mucus; of
both of which we have an example in catarrh or common cold, where, at
the beginning, the nostrils feel unusually dry, but as the disease
advances, the pituitary membrane becomes covered with a thick mucus:
in both states, the sense of smell is in general deficient, and
some