Good News for Mammals 153
off the entire healing limb, then fixed, stained, and sectioned it for the
DC STARTS LIMB REGENERATION IN RATS
I shall never forget looking at the first batch of specimens. The rat
had regrown a shaft of bone extending from the severed humerus. At the
proper length to complete the original bone there was a typical trans-
verse growth plate of cartilage, its complex anatomical structure per-
fectly regular. Beyond that was a fine-looking epiphysis, the articulated
knob at each end of a limb bone. Along the shaft were newly forming
muscles, blood vessels, and nerves. At least ten different kinds of cells
had differentiated out from the blastema, and we'd succeeded in getting
regeneration from a mammal to the same extent as Rose, Polezhaev,
Singer, and Smith had done in frogs.
Slides from some of the other animals were even more spectacular.
One stump had two cartilaginous deposits that looked like precursors of
the two lower arm bones beyond a fully formed elbow joint. All of the
regenerates were bent toward the electrode, and in one the lower
humerus had formed alongside the old shaft rather than as an extension
of
it,
but otherwise its structure was quite normal.
With one exception, slides from longer than a week were less excit-
ing. They seemed to have gotten less organized as time went on.
Behind
one of these older slastemas, at the end of a nearly unformed