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with a challenge to a duel, but Pasteur, evidently, did not care to risk dying that way and he sent Guérin's friends to the Secretary of the Academy with this message: "I am ready, having no right to act otherwise, to modify whatever the editors may consider as going beyond the rights of criticism and legitimate defense." And so Pasteur once more proved himself to be a human being—if not what is commonly called a man—by backing out of the fight.

As I have told you before, Pasteur had a great deal of the mystic in him. Often he bowed himself down before that mysterious Infinite—he worshiped the Infinite when he was not clutching at it like a baby reaching for the moon; but frequently, the moment one of his beautiful experiments had knocked another little chunk off that surrounding Unknown, he made the mistake of believing that all mysteries had dissolved away. It was so now—when he saw that he could really protect chickens perfectly against a fatal illness by his amazing trick of sticking a few of their own tamed assassins into them. At once Pasteur guessed: "Maybe these fowl-cholera microbes will guard chickens against other virulent diseases!" and promptly he inoculated some hens with his new vaccine of weakened fowl cholera germs and then injected them with some certainly murderous anthrax bacilli—and the chickens did not die!

Wildly excited he wrote to Dumas, his old professor, and hinted that the new fowl-cholera vaccine might be a wonderful Pan-Protector against all kinds of virulent maladies. "If this is confirmed," he wrote, "we can hope for the most important consequences, even in human maladies."

Old Dumas, greatly thrilled, had this letter published in the Reports of the Academy of Sciences, and there it stands, a sad monument to Pasteur's impetuousness, a blot on his record of reporting nothing but facts. So far as I can find, Pasteur never retracted this error, although he soon found that a vaccine made from one kind of bacillus does not protect an animal against all diseases, but only—and then not absolutely