106 TRANSACTIONS OF THE CANADIAN INSTITUTE. [VoL VIII. 
contraction of living protoplasm, and its general influence on the system, 
especially through the optic nerves, needed no confirmation. 
Nature’s defence against this injurious action of the chemical rays 
being pigmentation, the manner in which the pigment was laid down 
should lead to the discovery of the very part of the skin requiring protec- 
tion. In man, the pigment is placed in the deeper layers of the epidermis; 
there are no capillaries in the epidermis, but there are in the layer of skin 
immediately below it. In animals pigment cells are more scattered and 
often met with along the vessels of the skin. In reptiles complete tubes 
of pigment are seen around the vessels. From all of which it would appear 
that the blood vessels and the blood need protection. 
As to the absorption of light; it might be permitted to reason from 
a law in physics that only the light absorbed by bodies could act on these 
bodies, the chemical influence of light being in direct proportion to the 
light absorbed. Applying this law to the animal organism it is found 
that no living tissue absorbs so much light as the blood does, and, more 
than that, it absorbs a considerable quantity of the violet rays. 
Besides all the foregoing conclusions, other experiments showed him 
that light had a considerable influence upon the nervous system, at least 
in the lower animals. 
Having thus summed up his theoretical and practical evidence as 
to the irritant character of the chemical rays of light upon the healthy 
body, he reiterates the fact that his researches do not exclude the bene- 
ficial action of the chemical rays when in moderation, but regard the 
harmful action as due to exposure to too great a number of the rays, 
and for too long a time. 
Attention was then directed to acute diseases of the skin which 
might be produced by the chemical rays, and next to those diseases of 
the skin, which while not due to the chemical rays were unfavorably 
influenced by them. If chemical rays could produce a severe inflammation 
upon healthy skin it was most natural that they should exert an injurious 
influence upon a diseased skin. 
While deep in these researches and experiments, Finsen found in the 
library of the University of Copenhagen some articles bearing on the 
unfavorable action of light upon the course of small-pox. One of these 
was by Picton of New Orleans and published in 1832; it merely mentioned 
the fact that some soldiers confined in dark dungeons during a certain 
epidemic of small-pox, had contracted the disease and recovered without 
suppuration or scarring, but did not attempt to offer an explanation of 
the phenomenon. In 1867 and 1871 the English physicians, Black, 
