Le cœur mis à nu - continued...

But Czermak not only wanted his audience to see these movement-images, he wanted readers of the published lecture to see them as well. For this purpose, he designed a black disk with white points and lines.

When mounted on an axis, the cut-out disk (provided with slots at its periphery) allowed the reader to reproduce the movement of the light ray in the lecture hall. In front of a mirror, in a living room, for example, the view from the back side of the rotating disk through the slots depicted the up-and-down of the light spots induced by the movement of the beating frog heart.