The Body Electric - Micro-ondes

58 The Body Electric
THE NEUROEPIDERMAL JUNCTION
Rose had had, by pricking their limb stumps with a needle every day.
Polezhaev then found that a wide variety of irritants produced the same
effect, although none of them worked in mammals. His experiments
indicated that making the injury worse could make regeneration better,
and showed that Rose's salt-in-the-wound procedure worked by irrita-
tion rather than by preventing dermis growth.
Next, the part that nerve tissue played was clarified considerably by
Marcus Singer in a brilliant series of experiments at Harvard Medical
School from the mid-1940s to the mid-1950s. Singer first confirmed
Todd's long-forgotten work by cutting the nerves in salamander legs at
various stages of regrowth, proving that the nerves were needed only
in the first week, until the blastema was fully formed and the informa-
tion transferred. After that, regeneration proceeded even if the nerves
were cut.
Recent research had found that a salamander could replace its leg if all
the motor nerves were cut, but not without the sensory nerves. Many
assumed then that the growth factor was related only to sensory nerves,
but Singer was uneasy over this conclusion: "The problem stated in ad-
vance that one or another nerve component is all important for regenera-
tion." (Italics added.) Several facts didn't fit, however. Not only did the