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ing, even if you heat it gently, way below the point of boiling, the microbes that have no business in the wine will be killed—and the wine will not become sick. That little trick is now known to everybody by the name of pasteurization.

Now that people of the East of France had been shown how to keep their wine from going bad, the people of the middle of France clamored for Pasteur to come and save their vinegar-making industry. So he rushed down to Tours. He had got used to looking for microscopic beings in all kinds of things by now—he no longer groped as he had had to do at first; he approached the vinegar kegs, where wine was turning itself into vinegar, he saw a peculiar-looking scum on the surface of the liquor in the barrels. "That scum has to be there, otherwise we get no vinegar," explained the manufacturers. In a few weeks of swift, sure-fingered investigation that astonished the vinegar-makers and their wives, Pasteur found that the scum on the kegs was nothing more nor less than billions upon billions of microscopic creatures. He took off great sheets of this scum and tested it and weighed it and fussed with it, and at last he told an audience of vinegar-makers and their wives and families that the microbes which change wine to vinegar actually eat up and turn into vinegar ten thousand times their own weight of alcohol in a few days. What gigantic things these infinitely tiny beings can do—think of a man of two hundred pounds chopping two millions of pounds of wood in four days! It was by some such homely comparison as this one that he made microbes part of these humble people's lives, it was so that he made them respect these miserably small creatures; it was by pondering on their fiendish capacity for work that Pasteur himself got used to the idea that there was nothing so strange about a tiny beast, no larger than the microbe of vinegar, getting into an ox or an elephant or a man—and doing him to death. Before he left them he showed the people of Tours how to cultivate and care for those useful wee creatures that so strangely added oxygen to wine to turn it into vinegar—and millions of francs for them.