So Paul Ehrlich, in 1902, set out on his hunt. He got out his entire array of gleaming and glittering and shimmering dyes. “Splen-did!” he cried as he squatted before cupboards holding an astounding mosaic of sloppy bottles. He provided himself with plenty of the healthiest mice. He got himself a most earnest and diligent Japanese doctor, Shiga, to do the patient job of watching those mice, of snipping a bit off the ends of their tails to get a drop of blood to look for the trypanosomes, of snipping another bit off the ends of the same tails to get a drop of blood to inject into the next mouse--to do the job, in short, that it takes the industry and patience of a Japanese to do. The evil trypanosomes of the mal de Caderas came in a doomed guinea-pig from the Pasteur Institute in Paris; into the first mouse they went, and the hunt was on. They tried nearly five hundred dyes! What a completely unscientific hunter Paul Ehrlich was! It was like the first boatman hunting for the right kind of wood from which to make stout oars; it was like primitive blacksmiths clawing among metals for the best stuff from which to forge swords. It was, in short, the oldest of all the ways of man to get knowledge. It was the method of Trial and Sweating! Ehrlich tried; Shiga sweat. Their mice turned blue from this dye and yellow from that one, but the beastly finned trypanosomes of the mal de Caderas swarmed gayly in their veins, and killed those mice, one hundred out of every hundred! That man Ehrlich smoked more of his imported cigars, even at night in bed he would awake to smoke them; he drank more mineral water; he read in more books, and he threw books at the head of poor Kadereit--who heaven knows could not be blamed for not knowing what dye would kill trypanosomes. He said Latin phrases; he propounded amazing theories of what these dyes ought to do. Never had any searcher coined so many utterly wrong theories. But then, in 1903, came a day when one of these wrong explanations came to help him. Ehrlich was testing the pretty-colored but complicated benzopurpurin dyes on dying mice, but the mice were dying, with sickening regularity, from the mal de Caderas. Paul Ehrlich wrinkled his forehead--already it was like a corrugated iron roof from the perplexities and failures of twenty years--and he told Shiga: “These dyes do not spread enough through the mouse’s body! Maybe, my dear Shiga, if we change it a little--maybe, let us say, if we added sulfo-groups to this dye, it would dissolve better in the blood of the mouse!” Paul Ehrlich wrinkled his brow.