LIGHT AND LIFE. 305 



white rays exert an intermediate action. A long series of experiments 

 on birds satisfied Beclard that the quantity of carbonic acid thrown 

 out in breathing, during a given time, is not sensibly modified by the 

 different colors of the glasses the animals are placed under. It is the 

 same with small mammifers, such as mice ; but it is to be observed in 

 this case that the skin is covered either w T ith hair or feathers, and the 

 light does not strike the surface. The same plrysiologist examined 

 also the influence of the different-colored rays of the spectrum on 

 frogs. Under the green ray, the same weight of frogs produces in the 

 same period of time a greater quantity of carbonic acid than under 

 the red ray. The difference maybe a half greater; it is usually a 

 third or a fourth greater; but if the skin is afterward taken off the 

 frogs, and they are replaced under the same conditions, the result al- 

 ters. The amount of carbonic acid thrown out by the flayed frogs is 

 greater in red than in green light. A few experiments tried by Be- 

 clard on the exhalation of the vapor of water by the skin show that in 

 the dark, temperature and weight being alike, frogs lose by evapora- 

 tion a half or a third less moisture than under white light. In the 

 violet ray the quantity of moisture lost by the animal is perceptibly 

 the same as in white lisrht. 



Light acts directly on the iris of almost all animals, and thus pro- 

 duces contraction of the pupil, while heat produces the reverse phe- 

 nomena. This stimulus is observed in eyes that have been separated 

 for some time from the body, as Brown-Sequard has shown. 



Bert lately took up some very curious experiments on the prefer- 

 ence of animals for differently-colored rays. He took some of those 

 almost microscopic Crustacea, common enough in our fresh waters, the 

 daphne-fleas, remarkable for their eager way of hurrying toward light. 

 A number of these insects were put into a glass vessel, well darkened, 

 and a spectrum of the ray then thrown into it. The daphnes were 

 dispersed about the dark vessel. As soon as the spectrum-colors ap- 

 peared, they began to move, and gathered in the course of the lumi- 

 nous track, but, when a screen was interposed, they scattered agaiiu. 

 At first all the colors of the spectrum attracted them, but it was soon 

 noticed that they hurried much more toward the yellow and gree% 

 and even moved away a little if these rays were quickly replaced by 

 the violet. In the yellow, green, and orange parts of the spectrum 

 there was a thronging and remarkable attraction. A pretty large 

 number of these little beings were remarked in the red, too, a certain 

 number in the blue, and some, fewer in proportion to the distance, in 

 the most refrangible portions of the violet and ultra-violet. For these 

 insects, as for ourselves, the most luminous part of the spectrum was 

 also the most agreeable. They behaved in it as a man would do who, 

 if he wished to read in a spectrum thrown about him, would approach 

 the yellow and avoid the violet. This proves, in the first place, that 

 these insects see all the luminous rays that we see ourselves. Do they 

 vol. n. 20 



