But to push back old age? What is at the bottom of it? A Scandinavian scientist, Edgren, had made a deep study of the hardening of the arteries--that was the cause of old age, suggested Edgren, and among the causes of the hardening of the arteries were the drinking of alcohol, syphilis, and certain other diseases. “A man is as old as his arteries, that is true,” muttered Metchnikoff, and he decided to study the riddle of how that loathsome disease hardens the arteries. It was in 1903. He had just received a prize of five thousand francs, and Roux--who, though so different, so much more the searcher, had always stuck by this wild Metchnikoff--Roux had got the grand Osiris prize of one hundred thousand francs. Never were there two men so different in their ways of doing science, but they were alike in caring little for money, and together they decided to use all of these francs--and thirty thousand more which Metchnikoff had wheedled out of some rich Russians--to study that venereal plague, to attempt to give it to apes, to try to discover its then mysterious virus, to prevent it, to cure it if possible. And Metchnikoff wanted to study how syphilis hardened the arteries. So they bought apes with this money. French governors in the Congo sent black boys to scour the jungles for them, and presently large rooms at the Pasteur Institute were a-chatter with chimpanzees and orang-outangs, and the cries of these were drowned out by the shrieking of the sacred monkey of the Hindoos, and the caterwaulings of the comical little _Macacus cynemolgus_. Almost at once Roux and Metchnikoff made an important find; their experiments were ingenious and they had about them a certain tautness and clearness that was strangely un-Metchnikoffian. Their laboratory began to be the haunt of unfortunate men who had just got syphilis; from one of these they inoculated an ape--and the very first experiment was a success. The chimpanzee developed the disease. From then on, for more than four years they toiled, transmitting the diseases from one ape to another, looking for the sneaking slender microbe but not finding it, trying to find ways to weaken the virus--as Pasteur had done with the unknown germ of rabies--in order to discover a preventive vaccine. Their monkeys died miserably of pneumonia and consumption, they got loose and ran away. While Metchnikoff, not too deftly, scratched the horrible virus into them, the apes bit him and scratched him back--and then Metchnikoff did a strange and clever experiment. He scratched a little syphilitic virus into the ear of an ape, and twenty-four hours later he cut off that ear! The ape never showed one sign of the disease in any other part of his body.... “That means,” cried Metchnikoff, “that the germ lingers for hours at the spot where it gets into the body--now, as in men we know exactly where the virus gets in, maybe we can kill it before it ever spreads--since in this disease we know just when it gets in, too!”