Righting a Wrong Turn
217
tion decreases and cancer becomes more common. Although salamanders
stand about midway in degree of complexity, they're perhaps the least
specialized of all land vertebrates. They have tremendous regenerative
abilities and almost no cancer. Even to give them tumors in the labora-
tory requires much effort. Adult frogs, on the other hand, have bodies
that are much more specialized for their amphibious way of life; they
regenerate very little and are subject to several kinds of cancer.
AS REGENERATION DECREASES, CANCER INCREASES
In 1948 Meryl Rose decided to see whether the environment of a
salamander's regenerating limb could control the primitive cells of can-
cer as well as those of the blastema. He took pieces of a type of kidney
tumor common in frogs and transplanted them to the limbs of salaman-
ders. These tumors took better than most, and soon killed the animals
when allowed to spread unchecked. However, when Rose amputated the
leg just below or through the malignancy, normal regeneration fol-
lowed, and the cancer cells dedifferentiated more fully as the blastema
formed. Then as the new leg grew, the former frog tumor cells re-
differentiated along with the blastema. The frog cells were easily distin-
guished from salamander cells by their smaller nuclei, and microscopic
study showed frog muscle mixed in with salamander muscle, frog car-
tilage cells amid salamander cartilage, and so on.
This
monumentally
imporrant
experiment
proved
Rose's
hypothesis
that regeneration's guidance system could control cancer, too. It implied