Heat is the next important thing. You do not want a hothouse. Hot-houses are useful for growing delicate plants. Hot dwelling houses grow delicate people. The temperature of a house should be 68 or 70 degrees by a thermometer hung in the middle of the room. And it should be an even temperature, not 85 for a little while and then 60. So the fireman of the family should study the heating plant. The house may be heated by stoves, or by a hot-air, steam, or hot-water furnace. Different stoves and furnaces take different kinds of fuel, and different ways of managing them to get the best work from them at the least cost. Sometimes badly managed furnaces give off a poisonous gas that makes people ill. If the drafts are used properly, coal gases will go up the chimney.

Once in awhile you read about people being killed while asleep, with gas that escaped from a stove, a furnace, or a gas jet. This could not happen to people who sleep with the windows open, for the gas would go out of doors, but enough might collect in a well-ventilated house to make sleepers ill. No coal gas should escape from a furnace or stove, and gas pipes and burner keys should be tested often. Don't test them with a match, if you suspect a leak. Your nose is safer and just as reliable. You can always smell escaping gas. If you can't find the leak that way, send for a plumber. The leak may be from a pipe in a wall, or under a floor. A neglected leakage of gas may not only cause sickness, but also an explosion and fire.

Ventilation should be studied. Every house has windows and doors. Most of them have transoms over the doors. A few have fireplaces. Fireplaces are the best ventilators, even when there is no fire in them, for bad air is drawn up the chimney. A window, lowered from the top a few inches in cold weather, lets fresh air in between the sashes, and the bad air out above.

The time we need to be most careful about ventilation is in the winter. On cold winter evenings the family likes to sit in the cosy living room, warmed by the steam radiator or base burner stove. Two or three gas jets burn for reading or sewing. Fire and people use up the oxygen in the air very fast (see Air) and make carbon dioxide. In an hour or two the oxygen supply in the room gets too low for comfort, and the carbon dioxide too high.

Look for these danger signals Father begins to yawn. The lights do not burn so bright. Big brother feels dull and can't do his arithmetic. Sweet tempered sister gets cross The only bright and happy person in the room is the baby on the floor. The baby has the best air of all because warm, used air goes up. But even the baby cries after awhile; the canary bird nearly tumbles off its perch and mother has a headache The bad air almost fills the room. No one knows what is the matter. It's lucky if some one comes in from outside and says : "My, but it's stuffy in here." A window is opened and everyone brightens.

The next time that happens in your family, test the air in the room. Bring in a small glass jar of water and a bottle of lime water. Pour the water out of the jar and let it stand a few minutes to fill with the air in the room. Then pour a half inch of lime water in the jar and shake it hard to mix the air and water. If there is too much carbon dioxide in the room the water will turn chalky. The remedy is fresh air. Air as bad as that ought to be turned out of doors.

Every family should have a few simple "first aids for the injured" in the house, and know how to use them. A cut, a burn, a bruise, a bumped head or a bleeding nose, should be attended to without calling a doctor. Slight ailments, too, can be managed. Any family doctor, for the usual office visit fee, will tell you what things to keep on hand and how to use them. Better still, there are little books written by doctors telling "What to Do in Emergencies." Some of them cost only fifty cents, and can be kept in the medicine closet.

A house should be orderly, quiet and cheerful. Mother works hard to keep everything clean and in place. You know it is bad' for anyone to overwork. Most families thoughtlessly overwork the mother by throwing things around, and bringing dirt into the house. Perhaps that is why she is cross sometimes. She is not only overworked, she is worried because the work is never done. If it isn't good for you to lie awake and worry over examinations, it isn't good for mother to worry about how much extra work she has to do tomorrow.

Loud noises really hurt many people. Nerves need rest as well as bones and muscles, brains and stomachs. In cities, street cars and railroad trains, factory whistles and wagons and noisy crowds are always hammering at people's nerves. Homes are the places to rest nerves. So don't slam doors or scrape your chair legs on the floor, or throw your shoes across the room, or shout to someone upstairs. You may yell on a hundred-acre farm, or at a baseball game where everyone else is yelling. Very good people often quarrel and cry about little things, because their nerves are tormented all the time. Watch these danger signals. Sick nerves take a long, hard time to cure.

Finally, don't take all your troubles into the house to talk over. Long ago a great poet said: "A merry heart goes all the day, a sad tires in a mile-a." This is just as true as that two times two are four. Laugh and grow fat, and save doctor bills. Laughing exercises the lungs ; sour thoughts sour on the stomach. Bring all the cheerful things, the pleasant things, the funny things you come across, into the house. No family is as healthy as it might be unless it is happy.