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heads or tails of any of his little animals. After wiggling forward in one direction they stopped, they reversed themselves and swam backward just as swiftly without having turned around. But they must have heads and tails! They must have livers and brains and blood vessels as well! His thoughts floated back to his work of forty years before, when he had found that under his powerful lenses fleas and cheese mites, so crude and simple to the naked eye, had become as complicated and as perfect as human beings. But try as he would, with the best lenses he had, and those little animals in his mouth were just plain sticks of spheres or corkscrews. So he contented himself by calculating, for the Royal Society, what the diameter of the invisible blood vessels of his microbes must be—but mind you, he never for a moment hinted that he had seen such blood vessels; it only amused him to stagger his patrons by speculations of their unthinkable smallness.

If Antony Leeuwenhoek failed to see the germs that cause human disease, if he had too little imagination to predict the rôle of assassin for his wretched creatures, he did show that sub-visible beasts could devour and kill living beings much larger than they were themselves. He was fussing with mussels, shellfish that he dredged up out of the canals of Delft. He found thousands of them unborn inside their mothers. He tried to make these young ones develop outside their mothers in a glass of canal water. "I wonder," he muttered, "why our canals are not choked with mussels, when the mothers have each one so many young ones inside them!" Day after day he poked about in his glass of water with its slimy mass of embryos, he turned his lens on to them to see if they were growing—but what was this? Astounded he watched the fishy stuff disappear from between their shells—it was being gobbled up by thousands of tiny microbes that were attacking the mussels greedily. . . .

"Life lives on life—it is cruel, but it is God's will," he pondered. "And it is for our good, of course, because if there