LIGHT AS A BACTERICIDE. 
767 
filter are turned on the diseased region, which receives a bath 
of light. Using electric light, in preference to the snn, Mr. 
Finsen, after isolating the chemical rays, concentrates them 
with a lens. These purple light-baths last at least two hours, 
and the treatment is applied during several days, or several 
weeks, according to the cases. The spreading of the lesions is 
arrested and recoveiy goes on by degree. Applied only for the 
last two years, it is rather early to decide as to the value of the 
method, but the results so far obtained are very encouraging. 
It seems, however, that it would be worth while to apply the 
positive method in cases of variola, instead of the negative. 
Because, if the chemical rays can irritate the skin, as it is cer¬ 
tain they do, it is also very probable that they would act upon 
the microbes of* the vesicles, either close or open, and perhaps 
have a beneficial action. It is a question to study. As in both 
cases, the microbe is there, and it appears contradictory to allow 
it to grow in one case and to remove it from the active part of 
light by exposure to it in one case and destroy it in the other. 
A point which is interesting to consider is the indirect char¬ 
acter of the bactericide action of light. Whether it is the whole 
or the partial light represented by the chemically active rays, this 
action upon the microbes is not direct. It is indirect, as proved 
by Duclaux, d’Arcy and Hardy. The researches of the two 
last named, indeed, show that the antitoxic action of light takes 
place only in the presence of air. It seems, then, that the chemi¬ 
cal rays operate in giving rise to a reaction which has for con¬ 
sequence the formation of oxygen or perhaps of ozone, and then a 
slow oxidation. At any rate, the bactericide rays are precisely 
those which promote the formation of an oxidizing substance, 
as can be seen with the tetramethylparaphenyldiamined react¬ 
ing paper, which does not change color except for the rays be¬ 
tween the green-blue and the ultra-purple. And this is confirmed 
by numerous experiments which show that the destruction of 
bacteridies by light is accompanied by a consummation of air. 
Altogether, then, light or the chemical rays would kill bacilli 
in slowly burning them with oxygen. 
