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scientific speech on "The Curative Forces of the Organism" to the astonished doctors of the town. His delivery was superb; his sincerity was undoubted—but there is no record of whether or not he told the amazed doctors that he had not, up till then, so much as seen one phagocyte gobble up a single malignant microbe. Everybody—and this includes learned doctors—will stop to watch a dog fight; so this idea of Metchnikoff's, this story of our little white blood cells rushing to an endless series of Thermopylæs to man the pass against murderous germs—this yarn excited them, convinced them. . . .

But Metchnikoff knew he would have to have real evidence, and presently he found it, beautifully clear, in water fleas. For a time he forgot speeches and began fishing water fleas out of ponds and aquariums; here he was deucedly ingenious again, for these small animals, like starfish larvæ, were transparent so that he could see through his lens what went on inside them. For once he grew patient, and searched, like the real searcher that he so rarely was, for some disease that a water flea perchance might have. This history has already made it clear that microbe hunters usually find other things than they set out to look for—but Metchnikoff just now had different luck; he watched his water fleas in their aimless daily life, and suddenly, through his lens he saw one of these beasts swallow the sharp, needle-like spores of a dangerous yeast. Down into the wee gullet went these needles, through the walls of the flea's stomach they poked their sharp points, and into the tiny beast's body they glided. Then—how could the gods favor such a wild man so!—Metchnikoff saw the wandering cells of the water flea, the phagocytes of this creature, flow towards those perilous needles, surround them, eat them, melt them up, digest them. . . .

When—and this happened often too and so made his theory perfect—the phagocytes failed to go out to battle against the deadly yeast needles, these invaders budded rapidly into swarming yeasts, which in their turn ate the water flea, poisoned him—and that meant good-by to him!