At this meeting Robert Koch sat blinking at Pasteur behind his gold-rimmed spectacles and smiling under his weedy beard at such an unscientific inspirational address. Pasteur seemed to feel something hanging over him, and he challenged Koch to argue with him publicly--knowing that Koch was a much better microbe hunter than an argufier. “I will content myself with replying to Mr. Pasteur’s address in a written paper, in the near future,” said Koch--who coughed, and sat down. In a little while this reply appeared. It was dreadful. In this serio-comic answer Dr. Koch began by remarking that he had obtained some of this precious so-called anthrax vaccine from the agent of Mr. Pasteur. Did Mr. Pasteur say that his _first_ vaccine would kill mice, but not guinea-pigs? Dr. Koch had tested it, and it wouldn’t even kill mice. But some queer samples of it killed sheep! Did Mr. Pasteur maintain that his _second_ vaccine killed guinea-pigs but not rabbits? Dr. Koch had carefully tested this one too, and found that it often killed rabbits very promptly--and sometimes sheep, poor beasts! which Mr. Pasteur claimed it would guard from death. Did Mr. Pasteur really believe that his vaccines were really pure cultivations containing nothing but anthrax microbes? Dr. Koch had studied them carefully and found them to be veritable menageries of hideous scum-forming bacilli and strange cocci and other foreign creatures that had no business there. Finally, was Mr. Pasteur really burning so with a passion for truth? Then why hadn’t he told of the bad results as well as the good ones, that had followed the wholesale use of his vaccine? “Such goings-on are perhaps suitable for the advertising of a business house, but science should reject them vigorously,” finished Koch, drily, devastatingly. Then Pasteur went through the roof and answered Koch’s cool facts in an amazing paper with arguments that would not have fooled the jury of a country debating society. Did Koch dare to make believe that Pasteur’s vaccines were full of contaminating microbes? “For twenty years before Koch’s scientific birth in 1876, it has been my one occupation to isolate and grow microbes in a pure state, and therefore Koch’s insinuation that I do not know how to make pure cultivations cannot be taken seriously!” shouted Pasteur.