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The Body Electric
lose all powers of regeneration except fracture healing. What had hap-
Closer examination revealed that we'd made a hole in the skin when
we sutured the nerve to it. The nerve appeared to have grown into con-
tact with the epidermis. One of the requirements for normal regenera-
tion of a salamander limb was a neuroepidermal junction, and it looked
as though this had formed spontaneously in our one lucky rat when the
two tissues were brought together by surgery.
We changed the course of the experiment by operating on the other
rats to unite the sciatic nerve and epidermis, after scraping away the
dermis. We used animals of various ages. The results exceeded our ex-
pectations. Even the old rats regenerated their thighbones and much of
the surrounding tissue.
This offered an unparalleled opportunity to find out what it was about
the neuroepidermal junction that was so important. We prepared one
group of animals with a surgical neuroepidermal junction exactly as be-
fore. We prepared a second group the same way, except that we sutured
the nerve to the end of the bone, a millimeter away from the hole and
with no contact with the epidermis. The first group regenerated, while
the second group showed normal rat healing with no growth. The im-
portant observation, however, came
from electrical measurements we
made every day on the stumps. In those animals that formed a neu-
roepidermal junction, we found electrical potentials following the same
curve I'd found in the salamander. The voltage was about ten times as
high, but the pattern was exactly the same. In the animals having no
neuroepidermal junction, the potentials followed the same curve as in
the nonregenerating frog.
We'd discovered that the specific electrical
activity
that started
re-
generation was produced by the neuroepidermal
junction, not by the
simple bulk of nerve in the limb. My original that
the direct-