Nothing is truer than that there is no one orthodox way of hunting microbes, and the differences between the ways Koch and Pasteur went at their work are the best illustrations of this. Koch was as coldly logical as a text-book of geometry--he searched out his bacillus of tuberculosis with systematic experiments, and he thought of all the objections that doubters might make before such doubters knew that there was anything to have doubts about. Koch always recited his failures with just as much and no more enthusiasm than he did his triumphs. There was something inhumanly just and right about him and he looked at his own discoveries as if they had been those of another man of whom he was a little over-critical. But Pasteur! This man was a passionate groper whose head was incessantly inventing right theories and wrong guesses--shooting them out like a display of village fireworks going off bewilderingly by accident. Pasteur started hunting microbes of disease and punched into a boil on the back of the neck of one of his assistants and grew a germ from it and was sure it was the cause of boils; he hurried from these experiments to the hospital to find his chain microbes in the bodies of women dying with child-bed fever; from here he rushed out into the country to discover--but not to prove it precisely--that earthworms carry anthrax bacilli from the deep buried carcasses of cattle to the surface of the fields. He was a strange genius who seemed to need the energetic, gusto-ish doing of a dozen things at the same time--more or less accurately--in order to discover that grain of truth which lies at the bottom of most of his work. In this variety of simultaneous goings-on you can fairly feel Pasteur fumbling at a way of getting ahead of Koch. Koch had shown with beautiful clearness that germs cause disease, there is no doubt about that--but this isn’t the most important thing to do ... this is nothing, this proof, the thing to do is to find a way to prevent the germs from killing people, to protect mankind from death! “What impossible, what absurd experiments didn’t we discuss,” said Roux long after this distressing time when Pasteur was stumbling about in the dark. “We would laugh at them ourselves, next day.” To understand Pasteur, it is important to know his wild stabs and his failures as well as his triumphs. He had not the precise methods of growing microbes pure--it took the patience of Koch to devise such things--and one day to his disgust, Pasteur observed that a bottle of boiled urine in which he had planted anthrax bacilli was swarming with unbidden guests, contaminating microbes of the air that had sneaked in. The following morning he observed that there were no anthrax germs left at all; they had been completely choked out by the bacilli from the air.