Page:Popular Science Monthly Volume 20.djvu/71

Rh as oatmeal or burned arrow-root can do any harm, but, for sanitary purposes, such precautions must be supplemented by dental exercise. Let a child invigorate its teeth by chewing a hard crust, or, better yet, a handful of "St. John's bread" or carob-beans, the edible pod of the Mimosa siliqua. Children and whole tribes of the northern races seem to feel an instinctive desire to exercise their teeth upon some solid substance, as pet squirrels will gnaw the furniture if you give them nut-kernels instead of nuts. Thus Kohl tells us that the natives of southern Russia are addicted to the practice of chewing a vegetable product which he at first supposed to be pumpkin or melon seeds, but found to be the much harder seed of the Turkish sunflower (Helianthus perennis). Their national diet consists of milk, kukuruz (hominy, with butter, etc.), and boiled mutton, and they seem to feel that their Turkoman jaws need something more substantial. The schoolboy habit of gnawing pen-holders, finger-nails, etc., may have a similar significance. The Mimosa siliqua would yield abundantly in our Southern States, and its sweet pods would make an excellent substitute for chewing-gum. Our practice of sipping ice-cold and steaming-hot drinks, turn about, has also a very injurious effect upon the brittle substance that forms the enamel of our teeth; no porcelain glaze would stand such abuse for any length of time, and experience has taught hunters and dog-fanciers that it destroys even the bone crushing fangs of the animal from which our canine teeth derive their name.

Various diseases of the eye, including myopia, strumous and catarrhal ophthalmia, are due to a scrofulous diathesis, and sometimes to a general debility, and can be radically cured only by out-door exercise and a more nutritious diet. But a transient "weak-sightedness" (Schwach-sichtigkeit, as the Germans call it), is eminently a disease of the school-room, caused by a persistent abuse of the eyes, poring for hours together over a spelling-book or writing by the light of a flickering candle (much worse than twilight), as well as by the wretched print of our modern dictionaries and cheap cyclopædias. It should be kept in mind that reading and writing, even under the most favorable circumstances, require an effort to which the eye can only very gradually accustom itself. Hereditary influences and the preliminary exercises of the infant's eye, as, in examining picture-books, the first graphic essays with a slate-plencil, etc., may help to smooth the difficulty; for it is a fact, attested by the experience of all school-teaching missionaries, that the eyes of an adult, sharp-sighted savage begin to smart and water at the first attempt to decipher the hieroglyphics of his primer. The rudiments ought to be taught in half-hour lessons, with liberal intervals of rest and out-door play; and scrofulous children should never be sent to a public school till after a novitiate of at least six months of home studies. Instruct them never to pore over a book, but to keep the head erect, and, at the first symptoms of dim-