cal rays, and they only, had power to stimulate, to "stir
life." Finsen called it that himself. In the language of the
children, he was getting "warm."

That this power, like any other, had its perils, and that nature, if
not man, was awake to them, he proved by some simple experiments
with sunburn. He showed that the tan which boys so covet was the
defence the skin puts forth against the blue ray. The inflammation
of sunburn is succeeded by the brown pigmentation that henceforth
stands guard like the photographer's ruby window, protecting the
deeper layers of the skin. The black skin of the negro was no longer
a mystery. It is his protection against the fierce sunlight of the
tropics and the injurious effect of its chemical ray.

Searching the libraries in Copenhagen for the records of earlier
explorers in his field, and finding little enough there, Finsen came
across the report of an American army surgeon on a smallpox epidemic
in the South in the thirties of the last century. There were so many
sick in the fort that, every available room being filled, they had
to put some of the patients into the bomb-proof, to great
inconvenience all round, as it was entirely dark there. The doctor
noted incidentally that, as if to make up for it, the underground
patients got well sooner and escaped pitting. To him it was a
curious incident, nothing more. Upon Dr. Finsen, sitting there with
the seventy-five-year-old report from over the sea in his hand, it
burst with a flood of light: the patients got well without scarring
_because_ they were in the dark. Red light or darkness, it was all
the same. The point was that the chemical rays that could cause
sunburn on men climbing glaciers, and had power to irritate the sick
skin, were barred out. Within a month he jolted the medical world by
announcing that smallpox patients treated under red light would
recover readily and without disfigurement.

The learned scoffed. There were some of them who had read of the
practice in the Middle Ages of smothering smallpox patients in red
blankets, giving them red wine to drink and hanging the room with
scarlet. Finsen had not heard of it, and was much interested.
Evidently they had been groping toward the truth. How they came upon
the idea is not the only mystery of that strange day, for they knew
nothing of actinic rays or sunlight analyzed. But Finsen calmly
invited the test, which was speedy in coming.

They had smallpox in Bergen, Norway,