Page:Popular Science Monthly Volume 6.djvu/260

248 Borelly, studying the stability and displacement of fish, traced the plan of a divingship constructed upon the same principle as the formidable monitors which made their appearance in the recent American war.

"Aërial locomotion has always excited the strongest curiosity among mankind. How frequently has the question been raised, whether man must always continue to envy the bird and the insect their wings; whether he, too, may not one day travel through the air, as he now sails across the ocean! Authorities in science have declared at different periods, as the result of lengthy calculations, that this is a chimerical dream; but how many inventions have we seen realized which have also been pronounced impossible! The truth is, that all intervention by mathematics is premature, so long as the study of Nature and experiment have not furnished the precise data which alone can serve as a sound starting-point for calculations of this kind."

is a useful work on hygiene, and, as all intelligent hygienic action must be based upon some knowledge of the human subject, it opens with a description, in outline, of the composition of the body, of its various organs, the functions they perform, and the relations of food, exercise, and sleep. Then follows a consideration, in the natural order, of youth, maturity, and old age, with the dangers incident to each, and the precautions necessary.

In treating of the first stage, allusion is made to a danger little known and less heeded by people in general: this is, the effect upon children of violent outbursts of anger in parents and nurses. The young wife, by yielding to anger under the trials of her newly-assumed position, may doom her unborn babe to an imbecile existence. "The majority of imbeciles are first-born children, and their pitiful condition is the consequence of the mental perturbations during the term of pregnancy." Again: "In sucklings, too, mental disturbance in the mother or wet-nurse will commonly produce indigestion and diarrhœa in the baby." Nor does the danger end with infancy. Nearly every one has observed the deplorable influence which capricious paternal anger exercises upon children, some being made gloomy and morose thereby, others stubborn and revengeful. In connection with children advanced beyond the period of infancy, the author deplores the aversion, which they at the present day display, to eating fat, and recommends that parents should persistently endeavor to counteract it. He says: "Fat is most necessary to the proper growth of tissues, and, such being the case, is still more necessary to children." Without it, children grow up lean and spare.

The consideration of the causes of diseases in maturity is worthy of special attention. One of the most subtile of these causes, because little thought of, is the decay of the teeth. This is said to be on the increase, and is mainly attributed to excessive consumption of sugar, and the use of dentifrices. "Many dentifrices contain an acid which, by constantly eating away a thin surface of the enamel, keeps the teeth brilliantly white, but in time leads to their utter destruction."

Certain silly young ladies, who resort to the drinking of vinegar or the eating of raw rice, to avoid growing fat and florid, will be edified to learn that the amount of vinegar which will make them thin will destroy their digestive powers, and that a similar quantity of rice will produce habitual constipation, and prevent the assimilation of food.

In advanced life, many persons suffer much from inability to sleep. Moderate exercise during the day, and, at night, beds warmed before retiring, are recommended as the best remedies. In obstinate cases, a little alcoholic stimulant, mixed with warm water, may be taken to advantage just after entering bed. An important chapter is devoted to food and clothes, and another to stimulants and tobacco. The recent classification of alcohol as a food is adopted, and its use in small quantities considered harmless; in certain cases beneficial. Tobacco is also considered harmless in moderate quantities.

The chapter on mental strain, overwork, and tension, deserves a careful