Wait until your browser has finished loading the stack of images, on slow connections this can take some time. Scroll as you would normally on your PACS (hold down your left mouse button over the image and drag up or down). If nothing happens, it is still loading.

The javascript to enable this stack to scroll was provided by Daniel Cornfeld: Cornfeld D. A step-by-step solution for embedding user-controlled cines into educational Web pages. AJR Am J Roentgenol. 2008;190(3):W218–221.