BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic perspective view of a serial radiographic system having a pair of film changers according to the invention; FIG. 2 is a front view of one of the film changers of FIG. 1 showing components of the film changer in phantom outline; FIGS. 3a and 3b respectively are a perspective view of an X-ray film pack having a partially enclosed pouch and a