lessens the usefulness or incapacitates
the fine artist or skilful mechanic, in the prime of life, from
pursuing their vocations, may be, and is often, induced by the
influence of intoxicating drink, which debilitates and disorganizes the
brain.

3d. The tottering step, trembling hand, and shaking head of the aged
invalid, are the results of diminished nervous energy, so that steady
muscular contraction, so essential to regular movements, cannot be
maintained.

779. No difference can be discovered in the structure of the several
kinds of nerves in any part of their course, and the functions they
are designed to perform can only be known by ascertaining the place of
their origin. The nerves may be functionally divided into five
groups.

780. 1st. _Nerves of special sensation._ These are the first, second,
eighth, and it may be one of the branches of the fifth pair of cranial
nerves. The function of these nerves is particularly described in the
chapters upon the senses of smell, vision, hearing, and taste.

781. 2d. _Nerves of general sensation._ These embrace the fifth pair
of cranial nerves, and the thirty-one pairs of spinal nerves. In those
parts that require sensation for their safety and the performance of
their functions, there is an abundant supply of sensitive nervous
filaments. The nerves of sensation are mostly distributed upon the
skin. Few filaments ramify upon the mucous membranes and muscles.

_Observations._ 1st. The painful sensations experienced in the face,
and in the teeth or jaws, (tic douloureux and toothache,) are induced
by irritation and disease of a portion of the filaments of the fifth
pair of cranial nerves.

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The tremor of the hand among some mechanics in the prime of life? The
tottering step of the aged invalid? 779. What is said relative to the
structure of the nerves? How may they be divided? 780. Give the nerves
of special sense. 781. Those of general sensation. Where are the
nerves of sensation distributed? What causes tic douloureux?

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2d. The unpleasant sensation sometimes experienced when we hear the
grating of a file or saw, is produced by the connection of the nerve
that passes across the drum of the ear with the fifth cranial nerve.

3d. When pressure is made on the trunk of a nerve, the sensibility of
the part where the nerve ramifies is modified. This is illustrated,
when pressure is made upon the large nerve of t