f. Orton,[40] "more rapid in warm-blooded than in
cold-blooded animals, being nearly twice as fast in man as in the frog."
Wheatstone, by his method, gives the velocity of electricity in copper
wire at 62,000 geographical miles per second; but as neither Fizeau,
Gould, Gonnelle and others could arrive at the same result, the method
was shown to be incorrect, and it remained for Dr. Siemen[41] to
discover the true method, which gives the velocity just one-half that of
Wheatstone's estimate, or 31,000 geographical miles per second. In the
opinion of Bence Jones, the propagation of a nervous impulse is a sort
"of successive molecular polarization, like magnetism." But that this
agent is a force as analogous to electricity as is magnetism, is shown
not only by the fact that the transmission of electricity along a nerve
will cause the contraction of a muscle to which it leads, but also by
the important fact discovered by Marshall, that the contraction of a
muscle is excited by diminishing its normal electrical current,[42] a
result which could take place only with a stimulus, says Barker,
"closely allied to electricity. Nerve force must therefore be transmuted
potential energy." Prof. Huxley says,[43] "the results of recent
inquiries into the structure of the nervous system of animals, converge
toward the conclusion that the nerve-fibres which we have hitherto
regarded as ultimate elements of nervous tissue, are not such, but are
simply the visible aggregations of vastly more attenuated filaments, the
diameter of which dwindles down to the limits of our present microscopic
vision, greatly as these have been extended by modern improvements of
the microscope; and that a nerve is, in its essence, nothing but a
linear tract of specially modified protoplasm between two points of an
organism, one of which is able to affect the other by means of the
communication so established. Hence it is conceivable that even the
simplest living being may possess a nervous system."

Herbert Spencer[44] says all direct and indirect evidence "justifies us
in concluding that the nervous system consists of _one_ kind of matter.
In the gray tissue this matter exists in masses containing _corpuscles_,
which are soft and have granules dispersed through them, and which,
besides being thus unstably composed, are placed so as to be liable to
disturbances to the greatest degree. In the white tissue this matter is
collected together in extremely slender _thr