1904-5.] NIELS R. FinsEN—HiIs LIFE AND WORK. 103 
namely under the red glass, and Dubois in 1890 had shown that the proteus, 
an animal like the earthworm, preferring darkness, was least comfortable 
in white light. 
In 1851 Brucke had explained that the chameleon changed its colour 
by means of pigment cells in its skin, which came closer to the surface in 
light, and in darkness lay deeper; a slow change from darkness to light 
producing a scale of colouring in the animal which became successively 
whitish, gray-green, then spotted with black, and finally brownish-black ; 
the pigment cells in the skin of the animal being moved nearer to the sur- 
face to protect it against a disagreeable light impression. Paul Bert 
observed (1878) that red and yellow light had no influence on the pigment 
cells, while the blue and violet rays produce a strong reaction; and in 
1887 he observed further that if one-half the body of a chameleon were 
illuminated through a red glass, and the other half through a blue glass, 
the half under the red remains for a long time whitish, while the half under 
the blue glass becomes almost instantaneously blackish. 
Finsen had noticed that horses and horned cattle were subject to the 
so called ‘‘sun-burn”’ (solar erythema), as well as man, and many veteri- 
nary surgeons had informed him that this erythema was limited to non- | 
pigmented parts of the skin, almost exclusively. Wedding in 1883 had 
described an interesting observation, the truth of which had been confirmed 
by Virchow, namely, that cattle and sheep fed upon buckwheat are sub- 
ject to skin eruptions with the formation of vesicles, which was much more 
marked in the whiter animals and those exposed to the light or direct 
rays of the sun. Animals kept in the dark were not affected by the disease, 
and a white cow which had been coated on one side of its body with tar 
had the eruption on the opposite side only. An especially interesting 
observation had been made by Livius Furst, that when calves with a dark 
hide were vaccinated, in preparing animal vaccine, the pustules did not 
form well, and that consequently those with a light skin were preferred 
for the purpose. Volkmann in 1891 noted this fact as learned practically, 
but did not try to explain it. 
Moreover, Unna of Hamburg in 1885, Widmark of Stockholm in 
1889, and Hammer of Stuttgart in 1891 had definitely demonstrated 
that the chemical rays of the spectrum, and particularly the ultra-violet 
rays were responsible for erythema solare or eczema solare—commonly 
termed ‘‘sun-burn’’—and the pigmentation of the skin of human beings 
—or ‘‘tanning’’—and that these were not the effects of heat, for explorers 
in the polar regions and tourists on the glaciers, even when the tempera- 
ture is below zero may suffer severely from ‘‘sun-burn,” caused by the 
strong reflection of sunlight from the fields of ice. Widmark also demon- 
