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The Body Electric
There's still some opposition to parts of this scenario. Among some
scientists, the prejudice against electrobiology remains so strong that
one otherwise fine recent review doesn't even mention the NEJ or the
difference between currents of injury in frogs versus salamanders!
Other objections are a little more substantial. A Purdue University
group has measured electrical potentials near the surface of regenerating
limbs underwater, using a vibrating probe. This is an electrode whose
tip, ending in a tiny platinum ball, oscillates rapidly to and fro, giving
the average voltage between the two ends of its motion. These research-
ers describe an arc of ion flow—they categorically deny the possibility of
electron currents in living tissue—out from the stump and through the
water or, in semiaquatic animals, a film of moisture on the skin. From
the water, they suggest, these ions travel to the limb skin behind the
amputation, then in through all the inner tissues, and finally out of the
stump again to complete the circuit. They believe the epidermis drives
these currents by its normal amphibian function of pumping sodium
(positive) ions from the outside water into the body. They conceive of
this ion flow as the regeneration current itself, because changing the
concentration of sodium in the water directly affects their current mea-
surements, and because certain sodium-blocking techniques have inter-
fered with limb regrowth in about half of their experimental animals.
Of course, the Purdue researchers don't dispute the amply proven
need for nerve and injury currents during regeneration. They've even
confirmed Smith's induction of leg regrowth in frogs with batteries gen-
erating electron currents. Nevertheless, they consider nerves the target
rather than the source of current, even though they propose no reason
why their ion flow should be restricted to nerve tissue. In fact, they base
their hypothesis partly on evidence that sodium flows even from dener-
vated limbs.
There are several other problems with this theory: Its proponents' own
measurements show that the sodium ion current almost disappears just
when its supposed effect, blastema formation, is occurring. Moreover, it
fails to explain the easily observed reversal of polarity in injury currents
measured directly on the limb, as well as the crucial role of the NEJ.
The proposed circuit goes right past the NEJ! Finally, it can't account
for the several tests of semiconducting current throughout the nervous
system, or regeneration in dry-skinned animals such as lizards.
To the lay person all this may seem like academic hairsplitting, until
we reflect on the stakes: understanding regeneration well enough to re-
store it to ourselves. Certainly skin is electrically active. It's piezoelectric
and pyroelectric (turning heat into electricity) as well as a transporter of