  The physical principle of myelin development is obtained from our previous
study by explaining Peter's quadrant mystery: an external applied negative and
positive E-field can promote and inhibit the growth of the inner tongue of the
myelin sheath, respectively. In this study, this principle is considered as a
fundamental hypothesis, named Hypothesis-E, to explain more phenomena about
myelin development systematically. Specifically, the g-ratio and the fate of
the Schwann cell's differentiation are explained in terms of E-field. Moreover,
an experiment is proposed to validate this theory.
