For a while the searcher came uppermost in him. He forgot about possible savings of babies; he concentrated on vast butcheries of guinea-pigs and rabbits--he must prove that the diphtheria germ drips a toxin out of its wee body.... Together with Yersin he began a good unscientific fumbling at experiments; they were in the dark; there were no precedents nor any kind of knowledge to go by. No microbe hunter before them had ever separated a deadly poison (though Pasteur had once made something of a try at it) from the bodies of microbes. They were alone in the dark, Roux and Yersin--but they lighted matches.... “The bacilli _must_ pour out a poison into the broth we grow them in--just as they pour it from their membrane in a child’s throat into his blood!” Of course that last was not proved. Then Roux stopped arguing in a circle. He searched. He worked with his hands. It was worse, this fumbling of his, than trying to get a stalled motor to go when you know nothing about internal combustion machinery. He took big glass bottles and put pure microbeless soup into them, and sowed pure cultivations of the diphtheria bacillus in this broth; into the incubating oven went the large-bellied bottles----“Now we will try separating the germs from the soup in which they grow,” said Roux, after the bottle had ripened for four days. They rigged up a strange apparatus--it was a filter, shaped like a candle, only it was hollow, and made of fine porcelain that would let the soup through, but so tight-meshed that it would hold the tiniest bacilli back. With tongue-protruding care to keep themselves from being splashed with this deadly stuff, they poured the microbe-teeming broth around the candles held rigid in shiny glass cylinders. They fussed--maybe, or at least I hope so, with the blessed relief of profanity--but the broth wouldn’t run through the porcelain. But at last they pushed it through with high air pressure--and finally they breathed easy, arranging little flasks full of a clear, amber-colored filtered fluid (it had never a germ in it) on their laboratory bench. “This stuff should have the poison in it ... the filter has held back all the microbes--but this stuff should kill our animals,” muttered Roux. The laboratory buzzed with eager animal-boys getting ready the rabbits and guinea-pigs. Into the bellies of these beasts went the golden juice propelled from the syringe by Roux’s deft hands.... He became a murderer in his heart, this Émile Roux, and in his head as he came down to the laboratory each morning were half-mad wishes for the death of his beasts. “The stuff should be hitting them by now,” you can hear him growling to Yersin, but they looked in vain for the ruffled hair, the dragging hind legs, the cold shivering bodies to tell them their wish was coming true.