102 TRANSACTIONS OF THE CANADIAN INSTITUTE. [Vor. VIII. 
in degree only, notin kind. Thus, while all parts of the spectrum are cap- 
able of giving rise to heat, this quality is most marked towards the red and 
infra-red portion; also, while all parts of the spectrum are capable of giv- 
ing rise to chemical changes, this action is most marked, as a general rule, 
towards the blue, violet, but especially at the ultra-violet portion. And 
so we speak in general terms, if not quite correctly, of the heat rays, 
meaning thereby the red rays, and of the chemical or actinic rays, meaning 
the blue and violet rays. Red glass allows the red rays of light to pass 
through it, but absorbs the chemical rays, not permitting them to pass. 
This is why the ruby light is used in photography when one wishes to ex- 
amine a plate which would be spoiled if the chemical rays of daylight— 
‘‘white light’’—were allowed to reach it just then, but the red light is 
so weak in chemical action that it will affect the plate very slightly. Yel- 
low has the same deterrent effect on chemical rays. 
Much more than these bare facts was known to the world of science 
when Finsen, towards the close of his student life, began his experiments 
with light. His first investigations related to the injurious action of the 
so-called chemical rays of light, and with marvelous acumen he turned 
the researches of others to account; their results he was enabled to inter- 
pret, and their theories he was able to put to practical use. 
In one of his earliest contributions to medical literature in 1894 he 
admirably states the position of affairs up to that time as follows: ‘‘It 
must be acknowledged that, with the exception of the influence of light 
upon plants.and upon the organ of vision, our knowledge of the physiological 
action of light and its effects, whether good or bad, is very limited. In 
undertaking now the study of one of the properties of the chemical rays, 
viz., their injurious influence upon the animal organism, I do so, not 
because I regard this property as the only influence of the chemical rays, 
but because it constitutes the very foundation of our subject.’”’* In July, 
1893, he had set forth some striking theories with regard to the action of 
light,j and now he proposes to expound and elaborate them. 
He draws attention to the fact that the deleterious or fatal influence 
of light upon the majority of bacteria (germs) is already known, that one 
writer, Duclaux in 1885 had said that ‘‘sunlight is the best, cheapest, 
and most universally applicable bactericidal (7.e. germ-killing) agent 
that we have,”’ and others, for instance, Downes and Blunt in 1878 had 
shown that this effect was due almost exclusively to the chemical rays. 
It had been noted by Graber in 1883 that if earthworms (lumbrici) were 
placed in a box covered with strips of different coloured glass—using the 
colours of the spectrum—the worms always crawled to the darkest places, 
* Finsen, ‘‘ Phototherapy.” 
+ N. R. Finsen, ‘‘ Hospitalstidende,”’ July 5, 1893 
