Compared to this sly murderer the bacillus of anthrax had been reasonably easy to discover--it was a large bug as microbes go, and the bodies of sick animals were literally alive with anthrax germs when the beasts were about to die. But this tubercle germ--if indeed there was such a creature--was a different matter. Many searchers were looking in vain for it. Leeuwenhoek, with his sharpest of all eyes, would never have found it even if he had looked at a hundred sick lungs; Spallanzani’s microscopes would not have been good enough to have revealed this sly microbe; Pasteur, searcher that he was, had neither the precise methods of searching, nor, perhaps, the patience, to lay bare this assassin. All that was known about tuberculosis was that it must be caused by some kind of microbe, since it could be transmitted from sick men to healthy animals. An old Frenchman, Villemin, had pioneered in this work, and Cohnheim, the brilliant professor of Breslau, had found that he could give tuberculosis to rabbits--by putting a bit of the consumptive’s sick lung 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.