A century ago, two scientists exchanged fantastic microscope slides as Christmas cards

In the early 20th century, Arthur Earland and Edward Heron-Allen volunteered at what's now called the Natural History Museum, London (NHM). The two men spent their time researching fossils of single-celled organisms with shells, called Foraminifera, cataloging the various species, and creating microscope slides of the specimens. But each year when Christmas came around, they transformed their unique interest and skill into a fantastically fun gift exchange. From Smithsonian:

These Christmas-themed slides, which the two exchanged over their years of collaboration, had personalized greetings spelled out with microfossils (a term for fossils measuring under 1mm in size) that would be visible under a microscope. One from 1912 has Earland's initials ("AE"), "XMAS," and the year in an arrangement that measures about 1cm across.

Several examples of their Christmas slides are now in the collections of NHM. The 1912 slide is a part of the museum's touring exhibition Treasures of the Natural World alongside birds studied by Charles Darwin and an Iguanodon bone described by Richard Owen. More humble than these illustrious objects, the slide is still an incredible work of art and science, with each small fossilized shell carefully selected and delicately attached to the slide using a fine paint brush and Tragacanth gum...