INFLUENCE OF LIGHT ON ANIMALS. 327 
appear to undergo very remarkable modifications under the 
influence of the various coloured rays of the spectrum. Flies’ 
eggs ( Musca carnaria , Linn.) taken from the same groups and 
placed at the same time under variously coloured glasses, all 
produce worms. But if at the close of four or five days we 
compare the worms under the glasses, we remark that their 
development is very different. The most developed worms 
correspond to the violet and blue rays. The worms hatched 
under the green ray are the least developed. The various 
coloured rays may be grouped as follows with regard to the 
decreasing development of the w r orms : 
Violet, 
Blue, 
Red, 
Yellow, 
White, 
Green. 
The worms developed under the blue ray are three times 
larger, both in thickness and length, than those developed 
under the green ray. 
II. This first result led Us to examine the function which 
best shows the quantity of organic metamorphoses— we speak 
of the respiration — the products of which can be collected and 
estimatedi 
From a long series of experiments on birds, we find that 
the quantity of carbonic acid formed by the respiration in a 
given time, is not sensibly modified by the variously coloured 
glasses under which they were placed. It is the same with 
the small mammifera, such as the mouse. We must remark 
that among birds and the mammifera the skin is covered with 
feathers or hair, and that the light does not come in contact 
with its surface. Now we know from the researches of MM. 
Regnault and Reizet that the gaseous changes which take 
place on the surface of the bodies of these animals are 
almost nil . 
III. When w e examine the influence of the various coloured 
rays of the spectrum on frogs, whose skin is naked and 
whose cutaneous respiration is energetic (the cutaneous 
respiration equals and sometimes exceeds the pulmonary 
respiration), we prove remarkable facts. Our experiments 
have hitherto been only with the green ray and the red ray. 
We are now continuing them with the other rays. In the 
green ray an equal weight of frogs produces in the same 
time a much larger quantity of carbonic acid than in the red 
ray. The difference may be more than half ; it is generally 
at least a quarter or a third. 
