  It is proposed to search for scintillation of extragalactic sources through
the last unknown baryonic structures. Appropriate observation of the
scintillation process described here should allow one to detect column density
stochastic variations in cool Galactic molecular clouds of order of $\sim
3\times 10^{-5} \mathrm{g/cm^2}$ -- that is $10^{19} \mathrm{molecules/cm^2}$
-- per $\sim 10 000 \mathrm{km}$ transverse distance.
