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the microbes from our cultivations have killed twenty chickens out of twenty. . . ." But the time for his discovery was not yet, and next day, after these strangely recovered chickens had been put in charge of the caretaker, Pasteur and his family and Roux and Chamberland went off on their summer vacations. They forgot about those birds. . . .

But at last one day Pasteur told the laboratory servant: "Bring up some healthy birds, new chickens, and get them ready for inoculation."

"But we only have a couple of unused chickens left, Mr. Pasteur—remember, you used the last ones before you went away—you injected the old cultures into them, and they got sick but didn’t die?"

Pasteur made a few appropriate remarks about servants who neglected to keep a good supply of fresh chickens on hand. "Well, all right, bring up what new chickens you have left—and let's have a couple of those used ones too—the ones that had the cholera but got better. . . ."

The squawking birds were brought up. The assistant shot the soup with its myriads of germs into the breast muscles of the chickens—into the new ones, and into the ones that had got better! Roux and Chamberland came into the laboratory next morning—Pasteur was always there an hour or so ahead of them—they heard the muffled voice of their master shouting to them from the animal room below stairs:

"Roux, Chamberland, come down here—hurry!"

They found him pacing up and down before the chicken cages. "Look!" said Pasteur. "The new birds we shot yesterday—they're dead all right, as they ought to be. . . . But now see these chickens that recovered after we shot them with the old cultures last month. . . . They got the same murderous dose yesterday—but look at them—they have resisted the virulent dose perfectly . . . they are gay . . . they are eating!"

Roux and Chamberland were puzzled for a moment.

Then Pasteur raved: "But don't you see what this means?