Based on equation of electromagnetic induction for the magnetic flux density driven by Hall and Ohmic components of electric field generated by flows of thermal electrons an analytic model of helicoidal magneto-electron waves, whistlers, is developed. We found that the whistlers can propagate in the interstellar medium without noticeable attenuation. The presented numerical estimates for the group velocity of whistlers in the dark molecular clouds suggest that this kind of spiral circularly polarized magneto-electron waves can be responsible for the broadening of molecular lines detected from dark interstellar clouds.