Such was the gayety of Paul Ehrlich, and such his modesty--for he was always making straight-faced jokes at his own ridiculousness--that he easily won friends, and he was a crafty man too and saw to it that certain of these friends were men in high places. Presently, in 1896, he was director of a laboratory of his own; it was called the Royal Prussian Institute for Serum Testing. It was at Steglitz, near Berlin, and it had one little room that had been a bakery and another little room that had been a stable. “It is because we are not exact that we fail!” cried Ehrlich, remembering the bubble of the vaccines of Pasteur which had burst, and the balloon of the serums of Behring which had been pricked. “There must be mathematical laws to govern the doings of these poisons and vaccines and antitoxins!” he insisted, so this man with the erratic imagination walked up and down in those two dark rooms, smoking, explaining, expostulating, and measuring as accurately as God would let him with drops of poison broth and calibrated tubes of healing serum. But laws? He would make an experiment. It would turn out beautifully. “You see! here is the reason of it!” he would say, and draw a queer picture of what a toxin must look like and what the chemistry of a body cell must look like, but as he went on working, as regiments of guinea-pigs marched to their doom, Paul Ehrlich found more exceptions to his simple theories than agreements with them. That didn’t bother him, for, such was his imagination, that he invented new little supporting laws to take care of the exceptions, he drew stranger and stranger pictures, until his famous “Side-Chain” theory of immunity became a crazy puzzle, which could explain hardly anything, which could predict nothing at all. To his dying day Paul Ehrlich believed in his silly side-chain theory of immunity; from all parts of the world critics knocked that theory to smithereens--but he never gave it up; when he couldn’t find experiments to destroy his critics he argued at them with enormous hair-splittings like Duns Scotus and St. Thomas Aquinas. When he was beaten in these arguments at medical congresses it was his custom to curse--gayly--at his antagonist all the way home. “You see, my dear colleague!” he would cry, “that man is a SHAMELESS BADGER!” Every few minutes, at the top of his voice he yelled this, defying the indignant conductor to put him off the train.