The Swiss naturalist Conrad Gessner's 4,500-page encyclopedia of animals, the Historia Animalium, makes even the prolific Gilderoy Lockhart look like a slouch. Part fantasy, part observation, Gessner's dense and exuberant animal kingdom included creatures real and imaginary, running the gamut from sea monsters and whales to diminutive tabby cats. Of the unicorn, Gessner writes that its horn marrow, cut with a little wine, could heal a man who'd eaten a poisoned cherry, and could cure a number of ailments. All the better to keep young wizards out of the Hogwarts hospital wing.