A Crooke's Tube is a cold-cathode tube, wherein electrons are released from the cathode when ionised gas particles strike it with speed. Following a chain reaction, other gas particles also get ionised over time and do the same. But I guess there would be a time when all the gaseous atoms would have been ionised and travelled towards the cathode. So, no more electrons should be released now...and thus no cathode rays.
Or is there something happening, like the ionised atoms becoming normal again. It arises one more question in my mind....what happens to the ions after they strike the cathode?