72
The Body Electric
the inferior aquarium-bred stock but robust specimens collected from
their natural habitats.
Next I worked out some technical problems. The most important of
these was the question of where to place the electrodes. To form the
circuit, two electrodes had to touch the animal. One was the "hot" or
measuring electrode, which determined the polarity, positive or nega-
tive, with regard to a stationary reference electrode. A negative polarity
meant there were more electrons where the measuring electrode was
placed, while a positive polarity meant there were more at the reference
site. A steady preponderance of negative charge at a particular location
could mean there was a current flowing toward that spot, continually
replenishing the accumulation of electrons. The placement of the refer-
ence electrode, therefore, was critical, lest I get the voltage right but the
polarity, and hence the direction of the current, wrong. Some logical
position had to be chosen and used every time. Since I postulated that
the nerves were somehow related to the current, the cell bodies that sent
their nerve fibers into the limb seemed like a good reference point.
These cell bodies were in a section of the spinal cord called the brachial
enlargement, located just headward from where the arm joined the
body. In both frogs and salamanders, therefore, I put the measuring
electrode directly on the cut surface of the amputation stump and the
reference electrode on the skin over the brachial enlargement.
After setting up the equipment, I
did some preliminary measure-
ments on the intact animals. They all had areas of positive charge at the
brachial enlargement and a negative charge of about 8 to 10 millivolts at
each extremity, suggesting a flow of electrons from the head and trunk
out into the limbs and, in the salamanders, the tail.
I began the actual experiment by amputating the right forelimbs,
between elbow and wrist, from fourteen salamanders and fourteen grass
frogs, all under anesthesia. I took no special precautions against bleed-
ing, since blood clots formed very rapidly. The wounds had to be left
open, not only because closing the skin over the salamanders' amputa-
tion sites would have stopped regeneration, but also because I was in-
vestigating a natural process. In the wild, both frogs and salamanders
get injuries much like the one I was producing—both are favorite foods
of the freshwater bass—and heal them without a surgeon.
Once the anesthetic wore off and the blood clot formed, I took a
voltage reading from each stump. I was surprised to find that the polar-
ity at the crump reversed to positive right after the injury. By the next
day it had climbed to over 20 millivolts, the same in both frogs and
salamanders.