Man is a homoeothermic or warm-blooded creature. His normal body temperature remains almost constant in all the seasons. The temperature of the surroundings affects it very little. The normal temperature of a healthy person remains at 37°C or 98.4°F. As a result of this, the body remains warm. Do you know from where the heat energy comes to keep the body warm? Our body receives heat energy from the food we eat. The food substances produce heat by the process known as oxidation. Oxidation is a kind of combustion that takes place in our body. We know that the burning of fuels produces heat. The oxidation of food produces heat in the similar manner. The only difference is that burning of fuels produces both heat and light, while combustion of food produces only heat. The body uses the heat produced by food for doing different kinds of work. Foods such as flour, rice, sugar and potatoes contain sufficient quantity of carbohydrates. To consume foods containing carbohydrates is very important and necessary to the body because they keep body warm and provide it energy. Normally 2500 calories of heat energy is produced every day in the body of a human being. This energy keeps the body warm and enables its various organs to do different kinds of works. The ‘temperature centre’ of the brain maintains the temperature of the body. This centre consists of three parts — control centre that regulates the temperature of the blood; heating centre that raises the temperature of the blood when it drops; and the cooling centre that cools the blood when the temperature rises. Whenever a disturbance occurs in the temperature centre of the brain, the body starts shivering and this results in fever. If the disturbance occurs in the heating centre it causes shivering whereas the abnormality in the cooling centre causes fever in the body. The body always radiates heat to the surroundings. Whenever we sleep or sit on something, it becomes warm due to the heat coming out from our body. Many diseases cause a rise in body temperature. This happens because the body produces more heat than it can give off. Many disease-causing bacteria are killed by even a small increase in the person‘s body temperature. But if the body temperature rises above 44°C, it often results in death because some important enzymes are destroyed.