The Ticklish Gene
143
chamber. In four hours all the blood cells in the chamber had reactivated
their nuclei,
lost their hemoglobin,
and
become completely
unspe-
THE FIRST ARTIFICIAL DEDIFFERENTIATE
We repeated the experiment many times, working out the upper and
lower limits of the effective current. The best "window" was somewhere
between 200 and 700 picoamps. I say "somewhere" because the suscep-
tibility of the cells varied, depending on their age, the hormonal state of
the frog, and possibly other factors.* This was an infinitesimal tickle of
* Rather than continually renewing a small part of their red-cell stock, frogs generate a
whole year's supply in late winter as they emerge from hibernation. Thus, all their
erythrocytes age uniformly as the year progresses. The cells become less sensitive to
electricity as they get older, and that may be why frogs, even when warm and not
hibernating, heal fractures more slowly in winter. The red blood cells dedifferentiate
most readily in the spring, and the female's become even more sensitive than the male's
when she ovulates early in that season. At that time her red corpuscles will despecialize
in response to less than one picoamp. In fact, we saw red cells from ovulating females
dedifferentiate completely in chambers to which we supplied no current whatever. Ap-
parently an unmeasurably small current created by the charge difference between the
plastic chamber and glass cover slip was enough.