He injected little doses of the sheep serum into guinea-pigs; the next day he pumped virulent diphtheria bacilli into these same beasts. It was marvelous to watch them. There they were, scampering about with never a sign of sickness, while their companions (who had got no protecting dose of serum) perished miserably in a couple of days. How good it was to see them die, those unguarded beasts! For it was these creatures told him how well the serum saved the other ones. Hundreds of pretty experiments of this kind Behring made (there was little sloppiness now) and his helpers maybe pointed to their foreheads, asking whether their chief would ever have done saving one set of guinea-pigs and killing another set to prove he had saved the first. But Behring had reasons. “We made so many experiments because we wanted to show Herr Koch how far we had come in our immunizing of laboratory animals,” he wrote in one of his early reports. There was only one fly in the ointment of his success--the guarding action of the antitoxin serum didn’t last long. For a few days after guinea-pigs had got their injections of serum they stood big doses of the poison, but presently, in a week or two weeks, it took less and less of the toxin to kill them. Behring pulled at his beard: “This isn’t practical,” he muttered, “you couldn’t go around giving all the children of Germany a shot of sheep serum every few weeks!” And alas, his eagerness for something to make the authorities wide-eyed, led him away from his fine fussings with a way to prevent diphtheria--it sent him a-whoring after the pound of cure.... “Iodine tri-chloride is almost as bad for guinea-pigs as the microbes are--but this antitoxin serum, it doesn’t give them sores and ulcers.... I know it won’t hurt my animals.... I know it kills poison ... now, if it would cure!” Carefully he shot fatal doses of diphtheria bacilli into a lot of guinea-pigs. Next day, they were seedy. The second day their breath came anxiously. They stayed on their backs with that fatal laziness.... Then Behring took half of this lot of dying beasts, and into their bellies he injected a good heavy dose of the antitoxin from his immune sheep. Miracles! Nearly every one of them (but not all) began to breathe more easily in a little while. Next day, when he put them on their backs, they hopped nimbly back to their feet. They stayed there. By the fourth day they were as good as new, while their untreated companions, cold, dead, were being carried out by the animal boy.... The serum cured!