  Consistency of the Bekenstein bound on entropy requires the physical
dimensions of particles to grow with momentum as the particle is boosted to
transplanckian energies. In this paper the problem of particle growth in
heterotic string theory is mapped into a problem involving the properties of
BPS saturated black holes as the charge is increased. Explicit calculation
based on the black hole solutions of Sen are shown to lead to a growth pattern
consistent with the holographic speculation described in earlier work.
