Every one knows that instances of _catachresis_ occur in all languages;
but I think this case may be more satisfactorily explained by
considering that the _nerves_ consist of two very distinct and
independent classes of organs--nerves of sensation, which conduct
impressions to the sensorium; and nerves of volition, which convey the
mental impulse to the muscles. From this it necessarily follows that
when the former class are _over-active_ (and _redundancy_ is decidedly
the adjectival idea in the word _nervous_), a morbid excitability of
temper, with a perturbable anxious state of mind are produced (making
the "bad" sense of the word); while from a similar state of the nerves
of volition results a powerful and vigorous system of muscular action
and mental energy (making the "good" sense of the word).