( Originally Published 1917 )

Good Air and Bad Air.—The air of a closed room with many occupants is different in a number of ways from fresh outdoor air. The people in the room, by their breathing, have taken oxygen out of the air and given off into it carbon dioxide. Gas flames or lighted lamps also cause a decrease of oxygen and an increase of carbon dioxide. In the air of a crowded, poorly ventilated room, moreover, there is almost always a stale smell, which the people in the room may not notice after they have become used to it, but which any one coming in from outside notices at once. This smell comes from the mouths and bodies and clothes of the people.

The human body gives off not only carbon dioxide and these ill-smelling substances, but also heat and moisture. On the average, each person produces about as much heat as a candle flame; and the lungs and the skin together give to the atmosphere about three pints of water a day. If there were a candle burning in every seat in the schoolroom, the room would soon get warm; and so it does when there is a child sitting in each place, unless the heat is somehow carried away.

Both the heat and the moisture given off by the body are greatly increased by exercise, since the muscular work produces more heat, and the sweat glands form more perspiration to keep the body cool. It has been shown that a vigorous walk may cause an increase in heat production of i000 calories and an increase in evaporation of 800 grams. After a hard game, you generally want a drink of water to make up for the water lost in this way.

The Effect of Chemical Substances in the Air on Health.—It used to be thought that the air of a crowded room was bad because of its lack of oxygen and excess of carbon dioxide. Men who go down into mines or deep pits in the ground sometimes die because of lack of oxygen, just as a candle goes out in a closed space. This danger never arises, how-ever, in an ordinary room even when it is most crowded. Oxygen and carbon dioxide pass easily through cracks and even through walls and ceiling where there are no visible cracks, and there is never so little oxygen or so much carbon dioxide in a room as to harm any one.

The odors in the air of a close room are unpleasant, and experiments indicate that stale air has an unfavorable effect upon the appetite. It is important for the sake of health and decency that the air of schoolrooms and living rooms should always be kept fresh and free from unpleasant odors.

The Effect of a Warm Atmosphere on Health.—The worst thing about the air of a close room is its heat and, sometimes, its excess of moisture. A crowded, badly ventilated room is almost always a hot room, since human bodies produce heat and moisture as well as carbon dioxide. In such a room, the blood vessels in the skin expand and the blood goes to the surface of the body to cool off, as may be seen by the flushing of the face. The body temperature rises, the pulse goes up, and the blood pressure falls. As the blood moves to the outer surface of the body, the brain and other inner parts are robbed of blood, and one feels dull and listless and has little desire to work or play. In studies made by the New York State Commission on Ventilation, it was found that men did 15 per cent less work at 750, and 37 percent less work at 86°, than at 68°.

People who live in overheated rooms are likely to catch cold and to have other illnesses. In such people, the mucous membranes of the nose are constantly congested (filled with blood and lymph), as the blood vessels dilate to keep the body at the proper temperature. As a con-sequence, these membranes—instead of shrinking and drying promptly, as they should, when they come in con-tact with cold outer air—lose their quickness of response and stay moist and swollen after the blood vessels them-selves have contracted; this makes them an excellent breeding place for bacteria. ' People who have been weakened in this way are very sensitive to the cold air and are easily subject to chills. Benjamin Franklin once said, "People who live in the forest, in open barns, or with open windows, do not catch cold, and the disease called a cold is generally caused by impure air, lack of exercise, or from overeating"; and he was right.

The Value of Moving Air.—There is a great difference in the effect of still air and moving air, even when the general temperature is the same. The body is constantly giving off heat, and if the air is quiet, the portion close around the body will soon get much warmer than the rest, as if the body were surrounded by a kind of blanket of hot moist air. A wind breaks up this layer and brings fresh cool air to the body all the time; this is why it is so much more comfortable outdoors, or with an electric fan running, than in a closed room with still warm air.

Effects of Cold Air.—Moderate cold is a good thing for the body. It deepens the breathing, stimulates the blood vessels, and makes one feel active and vigorous—if the cold is not too great and does not last too long. Excessive cold is as bad, however, as excessive heat. Unless well wrapped up, it is dangerous for those not specially "hardened " to it to sit down or lie still in a room that is really chilly. Drafts, or local currents of cold air, on a particular part of the body seem to be especially harmful. It is most unwise to sit or stand in a cool place after you have been exercising hard and are flushed and moist with perspiration.

Chilling the body makes it less able to resist disease. If there happen to be germs of any kind in your nose or throat, the weakening effect of a chill may be just enough to give them a chance to grow and cause illness.

Effects of Atmospheric Humidity.—From what has been said in the last chapter, it will be obvious that on a hot moist day we feel more uncomfortable than on a hot dry day, because moisture interferes with the cooling effect of the evaporation of perspiration. At low temperatures the effect of moisture is quite different. When the air is cool, little perspiration is formed, and its evaporation is a small factor compared with the direct cooling caused by the cold air. This direct cooling will be favored by a humid atmosphere, since moisture collecting in the clothing increases its power of conducting heat. So it is a curious fact that humidity in the air makes a hot day hotter and a cold day colder.

Hot moist air is found in very crowded rooms and in certain factories, but most of our rooms in winter are hot and dry. The warmer the air is, the more moisture it can carry, and when we raise the temperature of cold air from outdoors to 60° or 70° without adding any moisture to it, it will become relatively much dryer or more ready to take up moisture.

Watching the Thermometer.—Unless children are provided with especially warm clothing, such as is used in open-air rooms, a temperature between 65° and 68° is generally right for 'the classroom. Every schoolroom and every living room should have a thermometer in it. It is a good plan in the classroom to have a pupil appointed each week to act as Health Officer and keep a record of the temperature hour by hour. When the thermometer gets to 70°, the windows should be opened to cool the air; for when-ever the temperature is above 70°, the work of the children will be affected and their health is likely to be injured.

Dusts and Poisons in the Air.—The ordinary fine dust in the air, which you can see as tiny flecks dancing in the sunbeam, does no harm. When a great cloud of dust is stirred up in sweeping, however, or when clouds of dust are whirled along by the wind in the street, there is real danger that any disease germs present may be carried and breathed into the nose or the mouth. This is why classrooms and corridors should never be swept when the children are in them. When you are on the street in a dust storm, keep your mouth shut so as to take in as little of it as possible.

The danger in breathing quantities of dust is not, how-ever, so much in the germs that the dust may contain as in the hard particles themselves, which may hurt the delicate lungs. Men who work at certain dusty trades, like steel grinding and granite cutting, easily fall victims to tuberculosis because their lungs have become injured by the inhaling of hard dust.

In other industries, such as white lead making and rubbing down paint, there are poisonous dusts or gases which may get into the air and do much harm. The only poison likely to be found in the air of houses is illuminating gas from leaking fixtures or from leaking or carelessly handled gas stoves. If there is the least smell about gas fixtures or stoves, or if the cocks are too tight or too loose, the gas man should be sent for; and great care should be taken not to leave cocks turned on unlighted or gas so low that it may blow out. A gas oven should never be lighted unless the door is wide open, because if, by any chance, gas has been escaping into the oven an explosion may occur.

What We Mean by Good Air.—Good air means air free from poisons or appreciable dust or objectionable odors. Above all, it means air that is not too warm or too cool and, if possible, in moderate and pleasant motion.

Heating and Ventilation.—Since cool, clean, fresh air is necessary for health, it is very important that the rooms in which we live and work should be well ventilated. Ventilation means a change of the air, or a supply of cool fresh air to take the place of that which has become stale and heated. About thirty cubic feet of fresh air per minute must be brought into a room for each person, in order that the bodily heat may be carried off and the air kept fresh and free from smell.

In warm weather and in a crowded room, where the heat from many bodies is considerable, overheating is the chief problem, and the air that enters should be cooler than the air in the room, so as to take up the excess heat. In cold weather, if a building has a system of direct heating by stoves or radiators in the room itself, the heating effect should be sufficient to balance the cool air admitted for ventilation. Some buildings are kept warm in winter by indirect heating, with warm air from a furnace or from a mechanical ventilating plant. In this case, the warm air sent into the rooms through the registers serves for both heating and ventilation, and should be at just the temperature, and in just the ?mount, to balance heat loss through the walls and yet keep the air of the room below 70°.

Methods of Ventilation.—The simplest way to get fresh air is to open the windows. Cold air is heavier than warm air and tends to fall, while warm air tends to rise. If a window is open at top and bottom and if it is cool outside, the warm air of the room will pass out at the top of the window, while the cool air from outside will enter at the bottom. If the wind is blowing, it may be a great aid in ventilation.

The trouble with window ventilation in winter is that the outside air is so much colder than the air indoors that it makes a draft near the windows, and persons sitting near them become too cool. Such drafts may be partially avoided by the use of sloping boards or glass plates made to fit into the bottom of the window, which direct the cool air upwards where it mixes with the air of the room. In very cold weather, a vertical board may be placed under the lower sash so that air comes in only between the sashes.

In some of the best schools, the ventilating and heating arrangements include sloping window plates, like those shown in Fig. 56, to direct the air upward; large radiators along the wall under the windows to warm the air some-what as it comes in; and ducts leading from near the ceiling out through the roof, to carry off the warm air which rises to the top of the room.

In small schools heated by stoves in the classrooms, the air often gets very stale if the windows are closed, while there are drafts if the windows are open. A sup-ply of fresh, but not too cold, air can be obtained, in such cases, by having a jacket around the stove with pipes leading in from the outer air to the lower part of the jacket. The heat of the stove will make an up-current and draw in fresh air through these pipes.

In larger school buildings, we usually find a system of indirect heating, fresh but warmed air being supplied by a mechanical ventilating system. This consists of a set of large ducts to bring warmed fresh air to each room and another set of ducts to take stale air out of each room, the air being driven through the ducts by revolving fans. Often this system is combined with radiators in the room, the system of heating then being called direct-indirect.

Whatever the ventilating system may be, it is a good plan to open all the windows now and then and take a little vigorous gymnastic exercise. The change to a low temperature for a few minutes makes you feel brisk and wide-awake, and the exercise makes the heart beat faster and the lungs take in more air. By exercising, you make sure that the body does not become chilled by the change in temperature.

Outdoor Life.—There is nothing quite so good as life out of doors. If you are to grow up to be as healthy as possible, you should be out of doors all you can. The wind breaks up the layer of warm air that clings close to the body, and the constant slight changes in temperature keep the skin in good condition, by stimulating its blood vessels and nerves so that they can quickly adjust themselves to changing conditions.

Fresh Air in the Bedroom.—It is especially important to have plenty of air in the sleeping room. Windows should be open at night, even in cold weather. Many people find that they grow stronger by sleeping on a porch in the open air. One should always take care, however, that there are enough covers on the bed to keep the body perfectly warm. It is dangerous to become chilled in sleeping.

QUESTIONS FOR DISCUSSION AND REVIEW

1. What is good air? Is the air better in the city or in the country? On a hilltop or in a hollow?

2. What changes take place in the air of an ill-ventilated, occupied room?

3. Why is the air at a moving picture show almost always bad? Why is it worse there than at a circus, where there are usually more people?

4. Why does bad air make one sleepy?

5. In -sweatshops in some of the larger cities, the workers sew all day in poorly ventilated, over-crowded rooms. Would you expect the workers to be strong, rosy, and well-grown? Explain.

6. In reports of Peary's Arctic journeys, it is said that the men had no colds until they returned to civilization. Explain.

7. Why do we have more colds in winter than in summer?

8. Which do you like better, a still day at 8o° or a windy day at 90°? Why?

9. Find out what you can of the punkahs in India. Why are they necessary?

10. Why is one likely to get chilled in going from an over-heated room into the cold, or standing in a draft when one is very warm from exercise?

11. Why is dust dangerous? The most up-to-date equipment in schools and offices calls for vacuum cleaners. Explain.

12. Why have big factories found it more economical, as well as more humane, to provide large, well-ventilated, well-lighted workrooms for their employees?

13. What trades do you know which are dangerous to the lungs because of fine substances in the air, which are inhaled by the workers?

14. How much air is needed for ventilation in your school-room?

15. Find out how your schoolroom is ventilated; whether by a mechanical system or by windows only; where the air comes in and goes out; and whether the system works well, so that the room never has a higher temperature than 68° and never gets stuffy and stale-smelling.

16. Explain what is meant by direct, indirect, and direct-indirect heating.

17. In the ventilation of a schoolroom, where would you place the inlet for fresh air and the outlet for stale air?

18. In many rural schools the only heat is from one big stove, and the only ventilation is at the windows. What are the draw-backs to this system? How may the system be modified?

19. Why do we exercise or play a game while the schoolroom windows are open to air the room?

20. There are many more open-air schools now than there were five years ago, and their number is increasing. What ad-vantage have they over ordinary schools?