Details of the process by which ionized pellet ablatant increases the density in a tokamak have been observed fcr the first time. For mild ablation rates, this process is not simply diffusive. Instead, the ionized ablatant takes the form of a temporally symmetric pulse which propagates over large distances along magnetic field lines. This pulse has been observed both interferometrically and with an x-ray camera. These observations are not in qualitative agreement with models which predict a step-like densification of the plasma by the pellet.