=Characteristics of a Vigorous Skin.=--A person who readily takes cold, who is fearful of drafts of air at all times, has a weak skin. To one who has a healthy skin drafts are dangerous only when the skin is moist with perspiration, and the body is inactive; cold drafts may then do harm. Cold air and cold water are the best means of toughening a tender skin. _A bath is to the skin what gymnastic exercises are to the muscles._ The muscle fibers in the walls of the blood vessels and the nerves controlling them need exercise as well as the rest of the body (Fig. 25). [Illustration: FIG. 25.--BLOOD VESSELS, with the VASO-MOTOR NERVES which accompany and control them.] =Importance of Bathing.=--_If we followed the outdoor life and wore the scanty clothing of savage races, the rains, the cool air, and the sunlight would keep our skins vigorous and sound._ But want of exercise to induce perspiration allows the sweat glands to become stopped up. The wearing of _clothes_ is a very uncleanly custom. Clothes make the skin inactive, yet confine the impurities which the weakened skin may still be able to excrete. Thick and heavy clothing and overheated rooms prevent the nerves from being stimulated by cold air and sunlight. _The best way to counteract these weakening conditions is by frequent cool or cold baths._ An _air bath_, which consists of exposing the bare skin to the air for half an hour or more before dressing in the morning, may take the place of a cold bath. Even the lower animals bathe: birds, dogs, and many lower animals bathe in the rivers. An elephant sometimes takes a bath by showering water over his back with his trunk. =Treatment of Burns.=--_Wet_ the burn with a little water and sprinkle common _baking soda_ or flour thickly on it. Bind with a narrow _bandage_. For deeper burns soak a small square of cloth in a strong solution of baking soda, bandage it on wound, and keep it wet with the solution. Olive, cotton seed, and linseed _oils_ are excellent for burns (Exp. 13). =Hygiene of Bathing.=--A bath should not be taken within an hour after a meal. _Cold baths_ (1) should never be taken in a cold room nor when the skin is cold; (2) are more beneficial in summer and in warm climates, but are necessary in winter for those who live in overheated houses or dress very warmly; (3) should be followed in winter by vigorous rubbing and a glowing reaction; (4) should usually not last longer than one minute in winter. _Warm baths_ (1) are more cleansing than cold baths; (2) should not be used alone but should always be followed by a dash of cold water; (3) are better than cold baths if the body is greatly fatigued; (4) are more beneficial when going to bed than upon rising.