They changed Atoxyl! They developed marvelous compounds of arsenic which--hurrah!--would really cure mice. “We have it!” the staff would be ready to shout, but then, worse luck, when the fell trypanosomes of the mal de Caderas had gone, those marvelous cures turned the blood of the cured mice to water, or killed them with a fatal jaundice.... And--who would believe it?--some of those arsenic remedies made mice dance, not for a minute but for the rest of their lives round and round they whirled, up and down they jumped. Satan himself could not have schemed a worse torture for creatures just saved from death. It seemed ridiculous, hopeless, to try to find a perfect cure. But Paul Ehrlich? He wrote: “It is very interesting that the only damage to the mice is that they become dancing mice. Those who visit my laboratory must be impressed by the great number of dancing mice it entertains....” He was a sanguine man! They invented countless compounds, and it was a business for despair. There was that strange affair of the arsenic fastness. When Ehrlich found that one big dose of a compound was too dangerous for his beasts, he tried to cure them by giving them a lot of little doses. But, curse it! The trypanosomes became _immune_ to the arsenic, and refused to be killed off at all, and the mice died in droves.... Such was the grim procession through the first five hundred and ninety-one compounds of arsenic. Paul Ehrlich kept cheering himself by telling himself fairy stories of marvelous new cures, stories that God and all nature could prove were lies. He drew absurd diagrams for Bertheim and the staff, pictures of imaginary arsenical remedies that they in their expert wisdom knew it was impossible to make. Everywhere he made pictures for his boys--who knew more than he did--on innumerable reams of paper, on the menu cards of restaurants and on picture post cards in beer halls. His men were aghast at his neglect of the impossible; they were encouraged by his indomitable mulishness. They said: “He is so enthusiastic!” and became enthusiastic with him. So, burning his candle at both ends, Paul Ehrlich came, in 1909, to his day of days. VI Burning his candle at both ends, for he was past fifty and his time was short, Paul Ehrlich stumbled onto the famous preparation 606--though you understand he could never have found it without the aid of that expert, Bertheim. Product of the most subtle chemical synthesis was this 606, dangerous to make because of the peril of explosions and fire from those constantly present ether vapors, and so hard to keep--the least trace of air changed it from a mild stuff to a terrible poison.