=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 serum of the blood also destroys the germs by the antitoxins in it. Inflammatory troubles are: colds, rheumatism, diarrhœa, and all diseases with name ending “_itis_.” An inflamed part is red, swollen, hot, and painful.