  From the Dirac sea concept, we infer that a body center cubic quark lattice
exists in the vacuum. Adapting the electron Dirac equation, we get a special
quark Dirac equation. Using its low-energy approximation, we deduced the rest
masses of the quarks: m(u)=930 Mev, m(d)=930 Mev, m(s)=1110 Mev, m(c)=2270 Mev
and m(b)=5530 Mev. We predict new excited quarks d$_S$(1390), u$_C$(6490) and
d$_b$(9950).
