“I have it!” he whispered, and called the busy Loeffler and the faithful Gaffky from their own spyings on other microbes. “Look!” Koch cried. “One little speck of tubercle I put into this beast six weeks ago--there could not have been more than a few hundred of those bacilli in that small bit--and now they’ve grown into billions! What devils they are, those germs--from that one place in the guinea-pig’s groin they have sneaked everywhere into his body, they have gnawed--they have grown through the walls of his arteries ... the blood has carried them into his bones ... into the farthest corner of his brain....” Now he went to hospitals everywhere in Berlin, and begged the bodies of men or women that had died of consumption, he spent dreary days in dead houses and every evening before his microscope in his laboratory where the stillness was broken only by the eerie purrings and scurryings of guinea-pigs. He injected the sick tissue from the wasted bodies of consumptives who had died, into hundreds of guinea-pigs, into rabbits and three dogs, thirteen scratching cats, ten flopping chickens and twelve pigeons. He didn’t stop with these wholesale insane inoculations but shot the same kind of deadly cheesy stuff into white mice and rats and field mice and into two marmots. Never in microbe hunting has there been such appalling thoroughness. “Ach! this is a little hard on the nerves, this work,” he muttered (thinking, perhaps of the lightning move of the paw of one of his cats jabbing the germ-filled syringe needle into his own hand). For Koch, hunting his invisible foes alone, there were so many disagreeable and always imminent possibilities of excitement--of something tragically worse than mere excitement.... But the hand of this completely unheroic looking little microbe hunter never slipped, it just grew drier and more wrinkled and blacker from its incessant baths in the bichloride of mercury--that good bichloride, with which in those old days the groping microbe hunters used to swab down everything, including their own persons. Then, week by week, in all of Koch’s meaouwing, crowing, barking, clucking menagerie of beasts those small curved bacilli grew into their relentless millions--and one by one the animals died, and gave eighteen-hour-days of work to Robert Koch in post-mortems and blear-eyed peerings through the microscope. “It is only when a man or beast has tuberculosis that I can find these blue-stained rods, these bacilli,” Koch told Loeffler and Gaffky. “In healthy animals--I have looked, you know, at hundreds of them--I never find them.” “That means, without doubt, that you have discovered the bacillus that is the cause, Herr Doktor----”