3. _Corns_ are thickened cuticle, caused by pressure or friction. They most frequently occur on the feet; but are produced on the shoemaker's knee by constant hammering, and on the soldier's shoulder by the rubbing of his musket. This hard portion irritates the sensitive cutis beneath, and so causes pain. A corn will soften in hot water, when it may be pared with a sharp knife. If the cause be removed, the corn will not return. 4. _Ingrowing Nails_ are caused by pressure, which forces the edge of the toe nail into the flesh. They may be cured by carefully cutting away the part which has mal-grown, and then scraping the back of the nail till it is thin, making a small incision in the center, at the top. The two portions, uniting, will draw away the nail from the flesh at the edge. Ingrowing nails may be prevented by wearing broad-toed shoes. 5. _Warts_ are overgrown papillæ (Fig. 24). They may generally be removed by the application of glacial acetic acid, or a drop of nitric acid, repeated until the entire structure is softened. Care must be taken to keep the acid from touching the neighboring skin. The capricious character of warts has given rise to the popular delusion concerning the influence of charms upon them. 6. _Chilblain_ is a local inflammation affecting generally the feet, the hands, or the lobes of the ear. Liability to it usually passes away with manhood. It is not caused by "freezing the feet," as many suppose, though attacks are brought on, or aggravated, by exposure to cold, followed by sudden warming. Chilblain is subject to daily congestion (see Congestion), manifested by itching, soreness, etc., commonly occurring at night. The best preventive is a uniform temperature, and careful protection against the cold by warm clothing, especially for the feet. PRACTICAL QUESTIONS. 1. If a hair be plucked out, will another grow in its place? 2. What causes the hair to "stand on end" when we are frightened? 3. Why is the skin roughened by riding in the cold? 4. Why is the back of a washerwoman's hand less water-soaked than the palm? 5. What would be the length of the perspiratory tubes in a single square inch of the palm, if placed end to end? 6. What colored clothing is best adapted to all seasons? 7. What is the effect of paint and powder on the skin? 8. Is waterproof clothing healthful for constant wear? 9. Why are rubbers cold to the feet? 10. Why does the heat seem oppressive when the air is moist? 11. Why is friction of the skin invigorating after a cold bath? 12. Why does the hair of domestic animals become roughened in winter? 13. Why do fowls spread their feathers before they perch for the night? 14. How can an extensive burn produce congestion of the lungs? 15. Why do we perspire so profusely after drinking cold water? 16. How can we best prevent skin diseases, colds, and rheumatism? 17. What causes the difference between the hard hand of a blacksmith and the soft hand of a woman?