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It can be understood from the passage that human nails ----.
French manicures and finding the end of the sticky tape;
if this is all you thought fingernails were good for, think
again. A new study explains why our nails are crucial to
our natural ability to grow back lost finger, and even
provides clues as to how we might enhance our limited
powers of regeneration. Although we might not be able
to grow whole fingers, we can regrow the ends of
amputated fingers. For years, scientists have wondered
why this only happens when some of the nail is left
behind. But now the answer has been discovered.
Studying mice, the biologists found stem cells – cells
that can change into any other kind – in a layer just
below the nail on mice toes. When the very tip of a toe
is amputated, a chain reaction is initiated that draws
nerves to the area. This in turn prompts the stem cells to
form new bone tendons and muscle. If a finger is
amputated too far back and there is no nail, this chain
reaction does not get started. It is thought that the same
mechanism is behind the regeneration of human
fingertips. “If we could identify all the molecules that
have this special ability to induce this kind of
regeneration, a pharmacological approach to treat
amputees might become available,” says the researcher
who led the study