A split counter arrangement was used to investigate the absorption coefficient of the radiation which causes the discharge to spread along the wire of a counter after the triggering of a pulse. The counters used were filled with methylene bromide and argon at various pressures, and with ethyl alcohol and argon. The results indicate that the vapor dissipates electron energies, thereby reducing the number of photons produced during the discharge. It was also observed that the absorption coefficient is a function of the argon alone, from which it was concluded that photo-ionization of the argon is responsible for spreading the discharge along the wire. This behavior was also observed with helium and neon in combination with alcohol or methylene bromide.