MOTHER: Yes, when we move quickly, we breathe faster, and the blood goes bounding through every part of the body, so the fire inside burns brightly. Sawing wood is a good way to warm a cold boy, and a broom is a fine helper to warm a cold girl. AMY: When it is frosty, we can see our breath. Is that the _smoke_ coming from the fire inside, mother? MOTHER: You may call it that if you like. When a candle burns, it gives off what we call carbonic acid gas, and we breathe out some of the same kind of gas. Water also comes out in the breath like steam from an engine, half a pint or a pint each day. ELMER: Do some kinds of food make more heat than others? [Illustration: “_A good way to warm a cold boy._”] [Illustration: “_A fine helper to warm a cold girl._”] MOTHER: Yes; all kinds of fatty foods make heat. In very cold countries people can eat more fat and keep well than in warm climates. Esquimaux eat a great deal of fat. A little Esquimau child would eat a tallow candle and enjoy it as much as you would an orange. I once read of some sailors who made a Christmas tree for some of those children in the frozen north. The tree was made of walrus bones tied together, and, instead of popcorn, fruit, and sweetmeats, they hung balls of fat on the tree. The children thought it a great treat, and ate them as quickly as you would eat peaches. AMY: How funny! But, mother, are not our bodies warmer in summer than in winter? MOTHER: You _feel_ warmer, it is true; but, no matter how hot or cold the weather may be, the body has always about the same warmth. I said _always_, but I mean when we are well. Sometimes we put the wrong kind of fuel into the furnace, and it makes a big fire, the house gets very hot, and we say we have a “fever.” If we get two or three degrees cooler than we should be, that shows that something is wrong, too. HELEN: But what keeps us the same whether it is hot or cold? [Illustration: “_We have a ‘fever.’_”] MOTHER: You know some stoves have dampers to govern the heat. When the body is in danger of becoming too warm, that is, when the body is well, all the little waste-pipes in the covering of our house pour out water so the skin is damp or moist, and if very warm it is wet. We might say we have thousands of little “dampers” to keep the heat just right. As the sweat dries, the body becomes cool; so in summer and in hot climates the people sweat much. In winter and in cold countries they perspire but little, and the tiny waste-pipes close as tightly as they can to keep the cold out and the heat inside. PERCY: But when I had a cold my skin was hot and dry. Why did not the little dampers make me cool, then? MOTHER: Because they were clogged so they could not. After a warm foot-bath and a hot lemon drink, you began to sweat and soon became well. If nothing had been done to open the waste-pipes, you might have had a serious illness.