Large (1.5 in. x 4.75 in.) microscope slides of animal tooth sections made by Joseph Bourgogne, a preeminent 19th century French slide-maker, in 1861. These difficult-to-make preparations represent some of Bourgogne's finest work. It is believed that these slides were some of the actual slides exhibited by Bourgogne at the International Exhibition in London in 1862. The mounting medium has darkened and turned a chocolate brown color over time. When new, they would have looked even more stunning, like modern X-ray images, for they were originally displayed mounted on black poster board. We know this because, amazingly, they still retain traces of glue and paper on their backs (which could easily have been cleaned off).