Page:Popular Science Monthly Volume 2.djvu/551

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pure water outside. In a word, a mutual exchange takes place between these two fluids, communicating by the membrane, and the current, passing from the thinner liquid toward the denser one, is ascertained to be more rapid than that moving in the opposite direction.

This experiment reveals one of the most important phenomena of life in plants and animals, noted by the word endosmosis. Now, Dutrochet had before observed that if the positive pole of a battery be inserted in the pure water, and the negative pole in the gum-water, the acts of endosmosis are effected more energetically. Oniraus and Legros discovered further, that, if the contrary arrangement be adopted, that is, if the positive pole be placed in the gum-water, and the negative pole in the pure, the level of the liquid in the tube descends noticeably, instead of rising. Electricity, therefore, can reverse the usual laws of endosmosis. It exerts an influence not less distinct on all the other physico-chemical movements, taking place deep in the organs. In them it decomposes the salts, coagulates the albuminoid elements of the blood and the tissues, just as it does in the vessels of the laboratory. Take a very curious instance: In chemistry, on decomposing the iodide of potassium, iodine is freed, and betrays itself by the tinge of intense blue which it develops on contact with starch. Now, if an animal be injected with a solution of iodide of potassium, and then electrified, it is noticed, after a few minutes, that all the parts near the positive pole of the battery turn blue in presence of the starch, proving that they are impregnated with iodine. The iodide has been almost instantly decomposed, and the iodine carried by the current toward the positive pole.

It is not surprising, then, that the action of electricity influences the whole system of the nutritive operations. Onimus and Legros found that ascending continuous currents quicken the twofold movement of assimilation and diassimilation. Animals electrified under certain conditions throw off a greater proportion of urea and carbonic acid, proving a higher energy of the vital fire. On the other hand, if young individuals, in growing development, are subjected to the action of the current, they grow tall and large more quickly than in ordinary circumstances, furnishing the proof of an increase in the quantity of substances assimilated. To show how far vital phenomena are stimulated by electricity, we will cite another experiment made by Robin and Legros on noctilucæ. These are microscopic animals, which, when existing in great numbers in sea-water, render it almost as white as milk, and at certain times phosphorescent. Now, a current, directed into a vessel filled with such water, suffices to bring out a trace of light marking all its course. Electricity stimulates the phosphorescence of all the noctilucæ met on its passage between the two poles.

Interrupted currents, or currents of induction, contract the blood--