But here were still some of those feeble but cured guinea-pigs, and Behring clutched at some good his murderous gropings might do. The gods were kind to him. He pondered, and at last he asked himself: “Will these cured animals be immune to diphtheria now?” He took these creatures and shot an enormous dose of diphtheria bacilli into them. They stood it! They never turned a hair at millions of bacilli, enough to kill a dozen ordinary animals. They were immune! Now Behring no longer trusted chemicals (think of the beasts that had gone down to the incinerator!) but he still had his fixed notion that blood was the most marvelous of the saps coursing through living things. He worshiped blood; his imagination gave it unheard-of excellences and strange virtues. So--with more or less discomfort to his decrepit cured guinea-pigs--he sucked a little blood with a syringe out of an artery in their necks; he let the tubes holding this blood stand until clear straw-colored serum rose over the red part of the blood. With care he drew this serum off with a tiny pipet--he mixed the serum with a quantity of virulent diphtheria bacilli: “Surely there is something in the blood of these creatures to make them so immune to diphtheria,” pondered Behring; “undoubtedly there is something in this serum to kill the diphtheria microbes....” He expected to see the germs shrivel up, to watch them die, but when he looked, through his microscope, he saw dancing masses of them--they were multiplying, “exuberantly multiplying,” he wrote in his notes with regret. But blood is wonderful stuff. Some way it must be at the bottom of his guinea-pigs’ immunity. “After all,” muttered Behring, “this Frenchman, Roux, has proved it isn’t the diphtheria germ but the poison it makes--it is the poison kills animals, and children.... Maybe these iodine-cured guinea-pigs are immune to the poison too!” He tried it. With sundry guttural gruntings, with a certain poetic sloppiness, Behring got ready a soup which held poison but had been freed of microbes. Huge doses of this stuff he pumped from a syringe under the hides of his decreasing number of desolate cured guinea-pigs. Again, they were immune! Their sores went on healing, they grew fat. The poison bothered them no more than had the bacilli which made it. Here was something entirely new in microbe hunting, something Roux maybe dreamed of but couldn’t make come true. Pasteur had guarded sheep against anthrax, and children from the bites of mad dogs, but here was something incredible--Behring, giving guinea-pigs diphtheria and then nearly killing them with his frightful cure, had made them proof against the microbe’s murderous toxin. He had made them immune to the stuff of which one ounce was enough to kill seventy-five thousand big dogs.... “Surely it is in the blood I will find this antidote which protects the creatures!” cried Behring.