  Using the soft pion theorem in the inclusive reactions, we estimate the soft
pion contribution to the structure functions $F_2$ and $g_1$ in the nucleon,
and show that it is an indispensable part in these structure functions in the
small $x$ region. This contribution is asymmetric for the soft $\pi^+$ and
$\pi^-$ due to pole terms in the soft pion limit, hence it is a remnant of the
spontaneous chiral symmetry breakings. Then we show that the modified strange
sea quark where the soft pion contribution is added to the distribution
determined by the ansatz (strange-sea)=(up-sea + down-sea)/4 satisfies the mean
charge sum rule for the sea quarks.
