Leeuwenhoek’s day of days had come. Alexander had gone to India and discovered huge elephants that no Greek had ever seen before--but those elephants were as commonplace to Hindus as horses were to Alexander. Cæsar had gone to England and come upon savages that opened his eyes with wonder--but these Britons were as ordinary to each other as Roman centurions were to Cæsar. Balboa? What were his proud feelings as he looked for the first time at the Pacific? Just the same that Ocean was as ordinary to a Central American Indian as the Mediterranean was to Balboa. But Leeuwenhoek? This janitor of Delft had stolen upon and peeped into a fantastic sub-visible world of little things, creatures that had lived, had bred, had battled, had died, completely hidden from and unknown to all men from the beginning of time. Beasts these were of a kind that ravaged and annihilated whole races of men ten million times larger than they were themselves. Beings these were, more terrible than fire-spitting dragons or hydra-headed monsters. They were silent assassins that murdered babes in warm cradles and kings in sheltered places. It was this invisible, insignificant, but implacable--and sometimes friendly--world that Leeuwenhoek had looked into for the first time of all men of all countries. This was Leeuwenhoek’s day of days.... III That man was so unashamed of his admirations and his surprises at a nature full of startling events and impossible things. How I wish I could take myself back, could bring you back, to that innocent time when men were just beginning to disbelieve in miracles and only starting to find still more miraculous facts. How marvelous it would be to step into that simple Dutchman’s shoes, to be inside his brain and body, to feel his excitement--it is almost nausea!--at his first peep at those cavorting “wretched beasties.” That was what he called them, and, as I have told you, this Leeuwenhoek was an unsure man. Those animals were too tremendously small to be true, they were too strange to be true. So he looked again, till his hands were cramped with holding his microscope and his eyes full of that smarting water that comes from too-long looking. But he was right! Here they were again, not one kind of little creature, but here was another, larger than the first, “moving about very nimbly because they were furnished with divers incredibly thin feet.” Wait! Here is a third kind--and a fourth, so tiny I can’t make out his shape. But he is alive! He goes about, dashing over great distances in this world of his water-drop in the little tube.... What nimble creatures! “They stop, they stand still as ’twere upon a point, and then turn themselves round with that swiftness, as we see a top turn round, the circumference they make being no bigger than that of a fine grain of sand.” So wrote Leeuwenhoek.