96
The Body Electric
caused by ionic discharges through the moist skin. If so, my evidence
was literally all wet.
Much of the uncertainty was due to the fact that I was measuring the
outside of the animal and assuming that generators and conductors inside
were making the pattern I found. I needed a way to relate inner currents
to outer potentials.
This was before transistors had
entirely replaced vacuum tubes. A
tube's characteristics depended on the structure of the electric field in-
side it, but to calculate the field parameters in advance without comput-
ers was a laborious task, so radio engineers often made an analog model.
They built a large mock-up of the tube, filled with a conducting solu-
tion. When current was applied to the model, the field could be mapped
by measuring the voltage at various points in the solution. I decided to
build a model salamander.
I made an analog of the creature's nervous system out of copper wires.
For the brain and nerve ganglia I used blobs of solder. Each junction was
thus a voltaic battery of two different metals, copper and the lead-tin
alloy of which the solder was made. Then I simply sandwiched this
"nervous system" between two pieces of sponge rubber cut in the shape
of a salamander, and soaked the model in a salt solution to approximate
body fluids and serve as the electrolyte, the conducting solution that
would enable the two metals to function as a battery. It worked. The
readings were almost exactly the same as in the real salamander. This
showed that a direct current inside could produce the potentials I was
getting on the outside.
If my proposed system was really a primitive part of the nervous sys-
tem, it should be widely distributed, so next I surveyed the whole ani-
mal
kingdom.
I
tested
flatworms,
earthworms,
fish,
amphibians,
reptiles, mammals, and humans. In each species the potentials on the
skin reflected the arrangement of the nervous system. In the worms and
fish, there was only one area of positive potential, just as there was only
one major nerve ganglion, the brain. In humans the entire head and
spinal region, with its massive concentration of neurons, was strongly
positive. The three specific areas of greatest positive potential were the
same as in the salamander: the brain, the brachial plexus between the
shoulder blades, and the lumbar enlargement at the base of the spinal
cord. In all vertebrates I also recorded a midline head potential that
suggested a direct current like that postulated by Gerard, flowing from
back to front through the middle of the brain. It looked as though the
current came from the reticular activating system, a network of cross-
linked neurons that fanned out from the brainstem into higher centers