  The paramagnetic insulator to ferromagnetic metal transition in Lanthanum
manganites and the associated magnetoresistive phenomena is treated by
considering the localization due to random hopping induced by slowly
fluctuating spin configurations and electron-electron interactions. The
transition temperature and its variation with composition is derived. The
primary effect of the magnetic field on transport is to alter the localization
length, an effect which is enhanced as the magnetic susceptibility increases.
Expressions for the conductivity, its variation with magnetic field, and its
connection with magnetic susceptibility in the paramagnetic phase are given and
can be tested with further experiments.
