There are questions of such vast, cosmic import that most of us never think to ask them. I’ve wondered why there’s something rather than nothing; I have pondered the nature of objectivity; I’ve questioned the existence of free will. But I’ve never asked why some hairs on my body grow in one direction, and other hairs an entirely different direction.

That’s where Walter Aubrey Kidd comes in. He was not like you or me; his was a mind so restive, so thick with a passion for inquiry, that no mystery, however impregnable, was safe from its advances. And so it was that in 1903 he bequeathed to us The Direction of Hair in Animals and Man, taking a fine-tooth comb to a subject most of us had hardly seen fit to tousle.

“No doubt many of the phenomena here described are intrinsically uninteresting and unimportant,” Kidd writes, with typical modesty, in his preface—but we know too well how important they are. Indeed, so does he: “The ultimate importance of it none can doubt,” he adds on the next page.

Otters, lions, dogs, horses, buffalo, donkeys, tapirs, deer, anteaters, chimpanzees, baboons, humans: Kidd looks at all of these and more in his quest to categorize, definitively, the patterns of hair growth among mammals. Over the course of 154 scintillant pages, no whorl, feathering, crest, or tuft eludes his powers of observation. He draws arrows. He examines pectoral regions, gluteal regions, deltoid regions. And my god, does he compare and contrast! Primarily, though, he imparts. Here he is imparting a fun fact about our very own bodies: reader, did you know that you’re almost entirely covered in hair?

Those who have not paid any particular attention to the matter are not aware that, in addition to the well-known hairy regions of the human body, every inch of skin is clad with fine hairs except the palms of the hands, soles of the feet, the ungual phalanges of the fingers and toes, and one or two small and unimportant areas.

Every sentence of The Direction of Hair in Animals and Man is that exciting. As for the illustrations, I’ll let them speak for themselves, though they are, in a way, vaguely NSFW. If you care to read on, you’re in luck: the whole book is free. You can start reading it right now.

Cancel your plans. The hair stream awaits.

Dan Piepenbring is the web editor of The Paris Review.