  In 1848 Pasteur conjectured that the rotation of the polarization plane of
the light in a dilute dielectric medium is generated by the molecular
symmetries of the medium where the light propagates. Our objective is to show
that Pasteur hypothesis was correct using basic knowledge of electromagnetism
and quantum mechanics. In Sections 2-5 we present a brief review of the
fundamental concepts of the electromagnetism necessary to study the optical
activity. In Sections 6-8 using the quantum mechanical perturbation theory and
taking into account the molecular symmetries we calculate the optical activity
of the medium. It will be shown that the theoretical predictions that are in
good agreement with the experimental results give support to the Pasteur
hypothesis.
