Le cœur mis à nu - continued...

A still-contracting heart cut out of a frog was posed on a small tripod. Small pieces of cork were placed on the two heart chambers. The cork pieces were connected with angled steel sticks. At the end of each stick was a light mirror plate that moved forward or backward when the corresponding heart chamber was contracting.

Czermak, 1879 (Projector)

By means of a device "similar to a laterna magica" (Czermak), a ray of light was directed onto both mirror plates. The plates reflected the light onto a screen. In the darkened lecture hall, the auditorium could see an enlarged image of heart movement.