Derived from the same basic cell layer, the ectoderm, that differentiates
into the nervous system, the eyes, hair, and teeth, the skin
retains a high sensitivity to the environment. Indeed, as a sensory
system-that is, a system that receives information from the environment-
the skin is much more important for survival than any of the
other sensory receptors. One can be born or become deaf and blind,
and survive and develop as a fine human being, as Helen Keller did;
but without a skin, there can be no survival at all.