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 vasomotor nerves which control the little muscle fibers in the walls of the blood vessels. The relaxing and enlarging of the blood vessels decreases the resistance to the blood flow, and the heart beats faster under its lighter load. The narcotic effect of alcohol is much more powerful than its irritating or stimulating effect. The effect of alcohol in causing fatty degeneration of the muscles often weakens the heart and other blood vessels.

Climate and Brain Work.—In going to sleep the vessels in the skin dilate and blood is drawn from the brain to the skin. It is difficult to go to sleep when cold, for cold sends the blood to the brain and keeps the mind active. On the same principle, mental work is difficult in very warm weather because of the enlarged capillaries in the skin and the withdrawal of blood from the brain to the skin. This increases the perspiration and keeps the temperature of the body down to normal, but it deprives the brain of blood needed for good mental work. Mental workers in warm weather and in warm climates should seek every condition favoring coolness. Benjamin Franklin was accustomed to strip himself almost entirely of clothing when he was writing and wanted his brain to work at its best. The wearing of barefoot sandals and the thinnest cotton clothing, light in color, helps to prevent mental inertia in hot weather. In the Gulf states in summer and in our tropical islands the best mental work can be done by rising at dawn and working before the hot part of the day begins. Some of the greatest thinkers in the world have lived in warm climates (Greece and India), but they wore very few clothes and ate moderately of the simplest food (see p. 44).

Congestion is a swelling of the blood vessels of some part, with the accumulation of blood therein. Congestion is active when a rapid flow of blood distends the capillaries. Example, flushing of face when running. Congestion is passive when there is a narrowing of the outlet of the capillaries, the blood moves slowly and partly stagnates in the swollen vessels. Example, when the nose feels stopped up during a cold. If a syringe is worked so fast that the rubber tube swells, this is like active congestion; if the end of the tube is pinched together so that moderate pumping causes it to swell, this is like passive congestion.

Inflammation is congestion where the vessels of any part are strained and injured. White corpuscles collect there to repair the vessels and devour the blood that escapes and stagnates there. They also destroy germs that have usually found lodgment and begun to multiply. The