This was Paul Ehrlich’s day of days. This was the magic bullet! And what a safe bullet! Of course there was no danger in it--look at all these cured rabbits! They had never turned a hair when Hata shot into their ear-veins doses of 606 three times as big as the amount that surely and promptly cured them. It was more marvelous than his dreams, which all searchers in Germany had smiled at. Now _he_ would laugh! “It is safe!” shouted Paul Ehrlich, and you can guess what visions floated into that too confident man’s imagination. “It is safe--perfectly safe!” he assured every one. But at night, sitting in the almost unbreathable fog of cigar smoke in his study, alone, among those piles of books and journals that heaped up fantastic shadows round him, sitting there before the pads of blue and green and yellow and orange note paper on which every night he scrawled hieroglyphic directions for the next day’s work of his scientific slaves, Paul Ehrlich, noted as a man of action, whispered: “Is it safe?” Arsenic is the favorite poison of murderers.... “But how wonderfully we have changed it!” Paul Ehrlich protested. What saves mice and rabbits might murder men.... “The step from the laboratory to the bedside is dangerous--but it must be taken!” answered Paul Ehrlich. You remember his gray eyes, that were so kind. But, heigho! Here was the next morning, the brave light of the bright morning. Here was the laboratory with its cured rabbits, here was that wizard, Bertheim--how he had twisted that arsenic through all these six hundred and six compounds. That man could not go wrong. So many of them had been dangerous that this six hundred and sixth one _must_ be safe.... Bravo! Here was the mixed good smell of a hundred experimental animals and a thousand chemicals. Here were all these men and women, how they believed in him! So, let’s go! Let us try it! At bottom Paul Ehrlich was a gambler, as who of the great line of the microbe hunters has not been? And before that sore on the scrotum of the first rabbit had shed its last scab, Paul Ehrlich had written to his friend, Dr. Konrad Alt: “Will you be so good as to try this new preparation, 606, on human beings with syphilis?” Of course Alt wrote back: “Certainly!” which any German doctor--for they are right hardy fellows--would have replied. [Illustration: LAST PORTRAIT OF EHRLICH]