  Traditionally, the interactions related to the 3D spatial angular momentum
have been studied completely, while the ones related to the generators of
Lorentz boost are always ignored. In this paper we show that the generators of
Lorentz boost have a nontrivial physical significance in quantum mechanics, and
try to propose a most general theory about electrical manipulations of electron
spin, where a new treatment and interpretation for the traditional Darwin term
and spin-orbit coupling is given via the concept of electron's induced electric
moment. Some electrostatic fields can even affect the spin quantum states of a
resting electron, and parallel electric and magnetic fields can be
simultaneously applied to fix on the spin orientation of electron.
