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into the front chamber of a rabbit's eye. Here Cohnheim could watch the little islands of sick tissue—the tubercles—spread and do their deadly work; it was a strange clever experiment that was like looking through a window at a disease growing. . . .

Koch had studied Cohnheim's experiments closely. "This is what I need," he meditated. "I may not use human beings for experimental animals, but now I can give the disease, whenever I wish, to animals . . . here is a real chance to study it, handle it, to look for the microbe that must cause it . . . there must be a microbe there. . . ."

So Koch set to work—he did everything with a cold system that gives one the shivers when one reads his scientific reports—and he got his first consumptive stuff from a powerful man, a laborer aged thirty-six. This man had been superbly healthy three weeks before, when all at once he began to cough, little pains shot through his chest, his body seemed literally to melt away. Four days after this poor fellow entered the hospital, he was dead, riddled with tubercles—every organ was peppered with little grayish-yellow, millet-seed-like specks——

With this dangerous stuff Koch set to work, alone, for Loeffler had set out to track down the microbe of diphtheria and Gaffky was busy trying to find the sub-visible author of typhoid fever. Koch, meanwhile, crushed the yellowish tubercles from the body of the dead man between two heated knives; he ground these granules up and delicately, with a little syringe, injected them into the eyes of numerous rabbits and under the skins of flocks of foolish guinea-pigs. He put these beasts in clean cages and tended them lovingly. And while he waited for his creatures to develop signs of the consumption, he began to peer with his most powerful microscope through the sick tissues that he had taken from the body of the dead workman.

For days he saw nothing. His best lenses, that magnified many hundred times, showed him only the dead ruins of what had once been good healthy lung or liver. "If there is a tuber-