The Ticklish Gene
139
most no nerves, were unaffected. Many piezoelectric materials emit a
continuous current for several hours after their charge-producing structure
has been left in a state of unresolved stress by fracture; I surmised that this
was true of bone and soon found that another research team had recently
proven it. Two separate currents, then, one from the nerves and one from
the bone matrix, were producing potentials of opposite polarity, which
acted like the electrodes of a battery. These living electrodes were creating
a complex field whose exact shape and strength reflected the position of
the bone pieces. The limb was, in effect, taking its own X ray.
While I was busy with my probes and meters, Dave was taking sam-
ples of the bones and blood clots and preparing them for the microscope.
We killed a few of the frogs every fifteen minutes during the first two
hours, then every day for two weeks, every other day for the third week,
and weekly for the last three weeks. Preparing the slides took several
days.
In the normal sequence of bone healing in frogs, a blood clot forms
after about two hours and develops into a blastema during the first
week. It turns into the rubbery, fibrous callus during the second and
third weeks, and ossifies in three to six weeks. In this last period, islands
of bone first emerge near the broken ends. Next, bony bridges appear,
connecting the islands. Then the whole area is gradually filled in and
organized with the proper marrow space and blood canals to join the
segments of old bone.
Dave began his work with specimens taken nearly a week after the
fractures, when we expected to see the first signs of the callus forming.
"This is mighty damn funny," he said as he walked in with the first box
of slides. "I can't see any mitoses in the periosteum. There's no evidence
that the cells there are multiplying or migrating."
We agreed that we must have done something wrong. Pritchard's
work had been quite conclusive on this point. He'd even published pho-
tographs of the periosteal cells dividing and moving into the gap. We
thought maybe we were looking at specimens from the wrong time
period, but we could see with our own eyes that the callus was starting
to form. Dave went back to study specimens from the first few days,
even though we didn't expect to see much then except clotting blood.
Soon he called me from his lab and asked, "What would you say if I told
you that the red corpuscles change and become the new bone-forming
cells?"
I groaned.
"Nonsense. That can't be right."
But it was right.
We
went over the whole slide series together. Beginning in the second hour,
the erythrocytes (red cells) began to change.