Page:Microbe Hunters.djvu/136

wee-est fragment of spleen, fresh out of a mouse that had a moment before died miserably of anthrax. Over the drop he put a thick oblong piece of glass with a concave well scooped out of it so that the drop would not be touched. Around this well he had smeared some vaseline to make the thin glass stick to the thick one. Then, dextrously, he turned this simple apparatus upside down, and presto!—here was his hanging-drop, his ox-eye fluid with its rod-swarming spleen, imprisoned in the well—away from all other microbes.

Koch did not know it, perhaps, but this—apart from that day when Leeuwenhoek first saw little animals in rain water—was a most important moment in microbe hunting, and in the fight of mankind against death.

"Nothing can get into that drop—only the rods are there—now we'll see if they will grow," whispered Koch as he slid his hanging-drop under the lens of his microscope; in a kind of stolid excitement he pulled up his chair and sat down to watch what would happen. In the gray circle of the field of his lens he could see only a few shreddy lumps of mouse spleen—they looked microscopically enormous—and here and there a very tiny rod floated among these shreds. He looked—fifty minutes out of each hour for two hours he looked, and nothing happened. But then a weird business began among the shreds of diseased spleen, an unearthly moving picture, a drama that made shivers shoot up and down his back.

The little drifting rods had begun to grow! Here were two where one had been before. There was one slowly stretching itself out into a tangled endless thread, pushing its snaky way across the whole diameter of the field of the lens—in a couple of hours the dead small chunks of spleen were completely hidden by the myriads of rods, the masses of thread that were