=Temperature Regulation.=--The temperature is regulated by variations in the production and loss of heat, less being known of its production than of its loss. It has been calculated that four-fifths of the energy of the body is converted into heat, one-fifth into work. As the minimum amount of heat produced in twenty-four hours is sufficient to raise 10 gallons of water from 0° to boiling-point, it is evident that if there were not some way for the escape of much of this heat the body would become hotter and hotter and finally destroy itself. The temperature, however, except on the surface, is uniform, heat being lost as fast as it is produced. For, although oxidation at any point raises the heat of the blood at the point, this heat is carried by the blood to other parts, to which the surplus is given up, while blood cooled in the skin goes to the hotter inward parts to cool them and be warmed itself. In fact, heat is expended by conduction and radiation, through respiration, perspiration, and heat given to the urine and fæces. It is, therefore, largely, 75 to 80 per cent., carried off through the skin and the lungs; 60 to 70 per cent. is lost by radiation to the air and other bodies with which the body comes in contact; 20 to 30 per cent. is lost by the evaporation of sweat, 4 to 8 per cent. by the warming of expired air, urine and feces, and 1 to 2 per cent. by cold food that is taken in. Radiation acts more favorably where the surroundings are cool and the air in motion, as on a breezy day. Conduction is carried on best where the surrounding air is cool, especially if it is moist, for moist air is a better conductor of heat than dry air. Evaporation is very important in hot weather or where men work in hot air. Even in health the temperature may range from 98.6° to 99.5°, and a degree or two below or above is not dangerous. When a person first gets up in the morning his temperature is apt to be subnormal, but after food and exercise have been taken it becomes normal and stays so till the end of the day, when, if the person is tired, it may go up a little. If a person is tired out, the temperature is apt to be subnormal. There is also in the body what is called the vital tide, which is highest afternoon and evening and lowest in the morning.