104 TRANSACTIONS OF THE CANADIAN INSTITUTE. [Vou. VIII. 
strated that the inflammation of the skin caused by a very strong electric 
light was identical with erythema solare. 
Finsen regarded pigmentation as nature’s way of protecting parts 
from the injurious action of the luminous rays, the colouring matter pre- 
venting the rays from penetrating too deeply and thus protecting the skin 
against their inflammatory action. Finsen proved this himself apart 
from any one else, and not knowing that others were experimenting in a 
similar direction. He was trying to account for the cause of the pig- 
mentation of the skin of negroes. To imitate the colour of the negro’s 
skin he painted a band of Indian ink about two inches wide on a part of 
his forearm not usually exposed to the sun, and normally quite light in 
colour, and exposed the arm to a very hot sun for about three hours. He 
then removed the Indian ink, and the skin under it was quite white still 
and normal, while that on either side was red. After a few hours inflam- 
mation, pain and slight swelling developed and lasted several days, and 
finally the parts became fairly strongly pigmented, but the protected por- 
tion remained normal throughout, even the little irregularities in the 
edges of the black band being clearly defined. The arm was then again 
exposed to. the sun, but without blackening it this time. The result was 
completely reversed; the white zone became the seat of the inflammation, 
while the parts on either side were not changed in appearance, except 
perhaps that they were a little more pigmented. Oarsmen who get their 
arms ‘“‘burned”’ early in the season, find the protection of the subsequent 
“‘tanning”’ later on. 
In animals, the surface most exposed to the sun is generally the most 
coloured; this is noticed in furred animals, whales, reptiles, birds, fish. 
Fish need this protection, because, while water absorbs the red and ultra- 
red rays to a high degree, it allows the ultra-violet to pass freely. ‘‘Among 
polar animals, pigmentation seems to vary in relation to light. There 
exists a connection between the black colours of the summer, which is so 
rich in light, and the whitish hues of the winter, which is so dark.’’* 
Too much light is injurious to plants, and provision is made by 
nature to protect them in various ways, a colouring matter being deposit- 
ed in certain cells for that purpose. 
The acute effects of the chemical rays upon human skin vary from 
a feeble irritation through all degrees up to inflammation followed by 
exfoliation, depending upon the intensity of the light and the proportion 
of chemical rays which it contains. Ordinary lamps give proportionately 
less, and electric light more chemical rays than the sun. The intensity 
* Finsen. 
