By this time the news of Koch’s discoveries had spread to all of the laboratories of Europe and had crossed the ocean and inflamed the doctors of America. The vast exciting Battle of the Germ Theory was on! Every medical man and Professor of Diseases who knew--or thought he knew--the top end from the bottom of a microscope set out to become a microbe hunter. Every week brought glad news of the supposed discovery of some new deadly microbe, surely the assassin of suffering from cancer or typhoid fever or consumption. One enthusiast would shout across continents that he had discovered a kind of pan-germ that caused all diseases from pneumonia to the pip--only to be forgotten for an idiot who might claim that he had proved one disease, let us say consumption, to be the result of the attack of a hundred different species of microbes. So great was the enthusiasm about germs--and the confusion--that Koch’s discoveries were in danger of being laughed into obscurity along with the vast magazines full of balderdash that were being printed on the subject of the germ theory. And yet to-day we demand with a great hue and cry more laboratories, more microbe hunters, better paid searchers to free us from the diseases that scourge us. How futile! For progress, God must send us a few more infernal marvelous searchers of the kind of Robert Koch. But in the midst of the danger that foolish enthusiasm would kill the new science of microbe hunting, Koch kept his head, and sat down to find a way to grow germs pure. “One germ, one kind of germ only, causes one definite kind of disease--every disease has its own specific microbe, I _know_ that,” said Koch--without knowing it. “I’ve got to find a sure easy method of growing one species of germ away from all other contaminating ones that are always threatening to sneak in!” But how to cage one kind of microbe? All manner of weird machines were being invented to try to keep different sorts of germs apart. Several microbe hunters devised apparatus so complicated that when they had finished building it they probably had already forgotten what they set out to invent it for. To keep stray germs of the air from falling into their bottles some heroic searchers did their inoculations in an actual rain of poisonous germicides! V Until, one day, Koch--who frankly admitted it was by accident--looked at the flat surface of half of a boiled potato left on a table in his laboratory. “What’s this, I wonder?” he muttered, as he stared at a curious collection of little colored droplets scattered on the surface of the potato. “Here’s a gray-colored drop, here’s a red one, there’s a yellow, a violet one--these little specks must be made up of germs from the air. I’ll have a look at them.” He stuck his short-sighted eyes down close to the potato so that his scraggly little beard almost dragged in it; he got ready his thin plates of glass and polished off the lenses of his microscope.