Page:Popular Science Monthly Volume 17.djvu/729

Rh are gold and silver, which are found in minute quantities, Iceland-spar, pure specimens of which are valued for optical instruments and cabinets, coarse chalcedonies and zeolites, lignite, basalt, and volcanic products. The manufacturing industry of the country is confined to woolen fabrics, socks and stockings, gloves, and a homespun cloth, which are excellent.

The Eyesight of Readers.—A writer in the "Library Journal" calls attention to the danger which readers run of injuring their eyesight by the use of a bad light. He remarks that engravers, watchmakers, and all others who use the eyes constantly in their work, take extra care to preserve them by getting the best possible light by day, and using the best artificial light at night. The great army of readers are care less, and have, sooner or later, to pay the penalty of their carelessness by giving up night-work entirely, and sometimes reading, except at short intervals and under the best conditions. All departures from common type, making the matter more difficult for the eye to take in, increase the danger. The magnitude of the physical labor of reading is not appreciated. A book of five hundred pages, forty lines to the page and fifty letters to the line, contains a million letters, all of which the eye has to take in, identify, and combine each with its neighbor. Yet many readers will go through such a book in a day. The task is one he would shrink from if he should stop to measure it beforehand. The best positions and best lights, clear type, plain inks, with the best paper of yellowish tints, and abundant space between the lines, afford the best safeguards against harm.

What Vivisection has done for Man.—Dr. Charles Richet, in a vigorous defense of the practice of vivisection, demands that it shall be judged by its practical results, and claims that, if it can be shown that we have gained by that method of experiment the means of curing one or two diseases of man or of assuaging pain, it must be considered lawful. He cites a number of discoveries that have been made through vivisection to sustain his position. Among them is the discovery of the circulation of the blood. Galen established the fact that the arteries contained blood by observations in the artery of a living animal; Harvey opened the chests of living animals, cut into the pericardium, observed the contraction of the heart, and what was going on in the veins and arteries, and deduced from what he saw his theory of the circulation. Transfusion of blood, an operation resorted to in extreme cases with the best results in saving life, was introduced after its possibility had been ascertained from experiments upon animals first made in 1664 by Lower and afterward by Denis. "Experiment alone," Dr. Richet says, "will teach us precisely what quantity of blood is necessary and what is harmful; and if over-sensitiveness forbids animal suffering for this end, then the experiments would have to be made on human beings." The mode of death from the inhalation of carbonic oxide, and, correlatively, the method of avoiding or preventing death from inhalation, have been made known only through vivisection. So also "all that we know in hygiene of the quantity of air necessary to support life is the result of experiments on dogs and rabbits. Sometimes a precise knowledge of the conditions of respiration has served to prevent men from perishing." Only two methods exist by which we may learn the conditions of gastric digestion and collect its secretion, viz., by observation of gastric fistulæ produced by chance in man, and by artificial fistulæ in animals. The first method has been possible only in three or four instances, but the effect of food on the gastric secretion in dogs and cats has been largely observed; and the knowledge of the remedies which have been applied to the relief of dyspepsia has been derived from such studies.' Our knowledge of nutrition has been largely added to by means of experiments in which dogs and cats have been submitted to varied alimentation, and from which the quantity and quality of food necessary to sustain life have been deduced. What we know of the nerves has been gained from studies of animals, as have also the means of relieving neuralgias and paralysis, in which, thanks to the scientific analyses of the vivisectors Fritsche, Hitzig, and Ferrier, "we can pass from the effect to the cause, and assign to paralysis a central lesion at a