continued posture, and not by any additional quantity of the spirit of
life; so we may conclude, that the passage of the electric fluid, which
produced a similar effect, acted only as a stimulus, and not by supplying
any addition of sensorial power.

If nevertheless this theory should ever become established, a stimulus must
be called an eductor of vital ether; which stimulus may consist of
sensation or volition, as in the electric eel, as well as in the appulses
of external bodies; and by drawing off the charges of vital fluid may
occasion the contraction or motions of the muscular fibres, and organs of
sense.

2. The immediate effect of the action of the spirit of animation or
sensorial power on the fibrous parts of the body, whether it acts in the
mode of irritation, sensation, volition, or association, is a contraction
of the animal fibre, according to the second law of animal causation. Sect.
IV. Thus the stimulus of the blood induces the contraction of the heart;
the agreeable taste of a strawberry produces the contraction of the muscles
of deglutition; the effort of the will contracts the muscles, which move
the limbs in walking; and by association other muscles of the trunk are
brought into contraction to preserve the balance of the body. The fibrous
extremities of the organs of sense have been shewn, by the ocular spectra
in Sect. III. to suffer similar contraction by each of the above modes of
excitation; and by their configurations to constitute our ideas.

3. After animal fibres have for some time been excited into contraction, a
relaxation succeeds, even though the exciting cause continues to act. In
respect to the irritative motions this is exemplified in the peristaltic
contractions of the bowels; which cease and are renewed alternately, though
the stimulus of the aliment continues to be uniformly applied; in the