It is strange but true that Dr. Finsen had never seen a smallpox patient at that time, but he knew the nature of the disease, and that the sufferer was affected by its eruption first and worst on the face and hands—that is to say, on the parts of the body exposed to the light—and he was as sure of his ground as was Leverrier when, fifty years before, he bade his fellow astronomers look in a particular spot of the heavens for an unknown planet that disturbed the movements of Uranus. And they found the one we call Neptune there. Presently all the world knew that the first definite step had been taken toward harnessing in the service of man the strange force in the sunlight that had been the object of so much speculation and conjecture. The next step followed naturally. In the published account of his early experiments Finsen foreshadows it in the words, “That the beginning has been made with the hurtful effects of this force is odd enough, since without doubt its beneficial effect is far greater.” His clear head had already asked the question: if the blue rays of the sun can penetrate deep enough into the skin to cause injury, why should they not be made to do police duty there, and catch and kill offending germs—in short, to heal? Finsen had demonstrated the correctness of the theory that the chemical rays have power to kill germs. But it happens that these are the rays that possess the least penetration. How to make them go deeper was the problem. By an experiment that is, in its simplicity, wholly characteristic of the man, he demonstrated that the red blood in the deeper layers of the skin was the obstacle. He placed a piece of photographic paper behind the lobe of his wife’s ears and concentrated powerful blue rays on the other side. Five minutes of exposure made no impression on the paper; it remained white. But when he squeezed all the blood out of the lobe, by pressing it between two pieces of glass, the paper was blackened in twenty seconds. That night Finsen knew that he had within his grasp that which would make him a rich man if he so chose. He had only to construct apparatus to condense the chemical rays and double their power many times, and to apply his discovery in medical practice. Wealth and fame would come quickly. He told the writer in his own simple way how he talked it over with his wife. They were poor. Finsen’s salary as a teacher at the university was something like $1200 a year. He was a sick man, and wealth would buy leisure and luxury. Children were growing up about them who needed care. They talked it out together, and resolutely turned their backs upon it all. Hand in hand they faced the world with their sacrifice. What remained of life to him was to be devoted to suffering mankind. That duty done, what came they would meet together. Wealth never came, but fame in full measure, and the love and gratitude of their fellow-men.