ron lie near each other without motion, and
afterwards approach each other; it is reasonable to conclude that something
besides the iron particles is the cause of their approximation; this
invisible something is termed magnetism. In the same manner, if the
particles, which compose an animal muscle, do not touch each other in the
relaxed state of the muscle, and are brought into contact during the
contraction of the muscle, it is reasonable to conclude, that some other
agent is the cause of this new approximation. For nothing can act, where it
does not exist; for to act includes to exist; and therefore the particles
of the muscular fibre (which in its state of relaxation are supposed not to
touch) cannot affect each other without the influence of some intermediate
agent; this agent is here termed the spirit of animation, or sensorial
power, but may with equal propriety be termed the power, which causes
contraction; or may be called by any other name, which the reader may
choose to affix to it.

The contraction of a muscular fibre may be compared to the following
electric experiment, which is here mentioned not as a philosophical
analogy, but as an illustration or simile to facilitate the conception of a
difficult subject. Let twenty very small Leyden phials properly coated be
hung in a row by fine silk threads at a small distance from each other; let
the internal charge of one phial be positive, and of the other negative
alternately, if a communication be made from the internal surface of the
first to the external surface of the last in the row, they will all of them
instantly approach each other, and thus shorten a line that might connect
them like a muscular fibre. See Botanic Garden, p. 1. Canto I. 1. 202, note
on Gymnotus.

The attractions of electricity or of magnetism do not apply philosophically
to the illustration of the contraction of animal fibres, since the force of
those attractions increases in some proportion inversely as the distance,
but in muscular motion there appears no difference in velocity or strength
during the beginning or end of the contraction, but what may be clearly
ascribed to the varying mechanic advantage in the approximation of one bone
to another. Nor can muscular motion be assimilated with greater
plausibility to the attraction of cohesion or elasticity; for in bending a
steel spring, as a small sword, a less force is required to bend it the
first inch than the second; and the second tha