Page:Popular Science Monthly Volume 2.djvu/318

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mulate in the organs. In the same way, for the sake of developing enormous fat livers in geese, they are put into dark cellars, kept entirely quiet, and crammed with meal.

Animals waste away as plants do. The absence of light sometimes makes them lose vigor, sometimes entirely changes them, and modifies their organization in the way least favorable to the full exercise of their vital powers. Those that live in caverns are like plants growing in cellars. In certain underground lakes of Lower Carniola we find very singular reptiles resembling salamanders, called proteans. They are nearly white, and have only the rudiments of eyes. If exposed to light they seem to suffer, and their skin takes a color. It is very likely that these beings have not always lived in the darkness to which they are now confined, and that the prolonged absence of light has destroyed the color of their skins and their visual organs. Beings thus deprived of day are exposed to all the weaknesses and ill effects of chlorosis and impoverishment of the blood. They grow puffy, like the colorless mushroom, unconscious of the healthy contact of luminous radiance.

William Edwards, to whom science owes so many researches into the action of natural agents, studied, about 1820, the influence exercised by light on the development of animals. He placed frogs' eggs in two vessels filled with water, one of which was transparent, and the other made impermeable to light, by a covering of black paper. The eggs exposed to light developed regularly; those in the dark vessel yielded nothing but rudiments of embryos. Then he put tadpoles in large vessels, some transparent, others shielded from the light. The tadpoles that were shone upon, soon underwent the change into the adult form, while the others either continued in the tadpole condition, or passed into the state of perfect frogs with great difficulty. Thirty years later, Moleschott performed some hundreds of experiments in examining how light modifies the quantity of carbonic acid thrown off in respiration. Operating on frogs, he found that the volume of gas exhaled by daylight exceeds by one-fourth the volume thrown off in darkness. He established, in a general way, that the production of carbonic acid increases in proportion to the intensity of light. Tims, with an intensity represented by 3.27, he obtained 1 of carbonic acid, and, with an intensity of 7.38, he obtained 1.18. The same physiologist thinks that in batrachians the intensity of light is communicated partly by the skin, partly by the eyes.

Jules Béclard made more thorough researches. Common flies' eggs, taken from the same group, and placed at the same time under differently-colored glasses, all produce worms. But if the worms, hatched under the different glasses, are compared at the end of four or five days, perceptible differences may be seen among them. Those most developed correspond with the violet and blue ray; those hatched under the green ray are far less advanced; while the red, yellow, and