ascinating microscopic discovery!
In the late 1800s, naturalists were fascinated by the new world of diatoms which had opened up to them by way of the light microscope. Expeditions were staged to collect and trade exotic forms from around the world. The Germans Thum, Möller, and Elger began creating slides of arranged diatoms which were traded worldwide. These slides are still valued by collectors today.

"The richness of this slide is astounding. They are grouped in families, and it is thus easy to compare the different families together, and note what characteristics their species bear in common, and how they differ from other groups. We cannot imagine that any large number of slides, requiring such a remarkable combination of patience and skill, will be issued. Ours is numbered thirty, and we do not envy the preparer his laborious job. We used to think a good deal of a half a dozen or a dozen diatoms elegantly arranged; but to persuade hundreds of these minute objects to stand in order, with military precision, was what we never expected to see. Of course there will be many who will desire to possess this slide, simply on account of its rarity and beauty; but its scientific value will also be appreciated, and we trust microscopists will not underrate the value of a systematic collection because they have it on a single piece of glass, instead of scattered through a cabinet full of drawers." -1869 Excerpt from "The student and intellectual observer of Science, Literature and Art"