CHAPTER V.

THE NECESSITY OF FRESH AIR.

"I would speak in especial of a chamber which I once entered, as I had often before entered it, early one winter's morn. It was the sleeping closet of my son. His low trestle bed stood betwixt the severally widely open window and door, while the keen but exquisitely fresh sweet atmosphere from windswept hills careered through the apartment ceaselessly. The hue of exuberant health mantled over the boy's every feature, while bordering the margin of the coverlet there extended a fringe of pure white snow which the genius of the fragrant night had wafted in, all harmlessly, during the hours of my child's repose."-Spoken of the late Sir WILLIAM MACCORMAC, President of the Royal College of Surgeons of England.

'The mistake of most modern ventilation is that there is not enough of it.”—The Treatment of Phthisis, ARTHUR RANSOME, M.D., F.R.S.

THE breathing of fresh air is essential to healthy

life. We all know that the circulating blood in the human body is the means by which food (proteins, sugar, starch, fat, etc.) and oxygen are carried to the tissues and organs of all parts of the body. The food is picked up by the blood from the digestive system, the oxygen is picked up in

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the lungs from the air which we breathe. The flesh and organs of the body use up this oxygen which is thus brought to them by the blood, and empty back into the blood, so to speak, their own waste products. The blood therefore not only brings oxygen to the tissues but carries away some of the waste materials which it gets rid of in the lungs. The lungs are thus the great centre of exchange. It is in the air cells of the lungs that the blood is brought into direct contact with the air which has been breathed in. It is there that it gives up its burden of waste products (carbonic acid gas, water, organic matter, ammonia, etc.) and takes in its new quantities of oxygen. If it cannot make this exchange the blood becomes impure and of poor quality, and the whole body suffers in consequence.

It is upon this simple principle of physiology that the need of fresh air, and therefore of ventilation, is based. To understand the elements of this subject it is necessary to consider what is the usual composition of the atmosphere, its effects on health, what are its physical properties, and then finally what are the principles and means of ventilation.

The Composition of the Atmosphere.

Fresh air is a mixture of certain gases, some water, and a small amount of solid matter in the form of very fine particles. Its chief gas in amount is nitrogen, an invisible, tasteless, odourless gas, which from the point of view of public health is important only as a diluent of the air. By far the most important gas present is oxygen, which is also a colourless, tasteless gas, which burns up any organic matter exposed to it. It is increased in quantity by vegetation and by

rain, but decreased by respiration of man and animals, by combustion (the burning of fires and lights), by organic effluvia, and by fog. The average quantity present in air is twenty-one per cent. Then, thirdly, there is carbonic acid gas or CO, (about .04 per cent.) which differs from the other two in being poisonous if breathed in large amounts. This gas is also increased in confined spaces by respiration, combustion, decomposition, and fog, and it is diminished by vegetation, which absorbs it, by rain, by high winds, and of course, by ventilation. There is more in town atmosphere than in the country and more still in "close" rooms and tunnels. Ammonia is also present in air, and marsh gas (in mines) and compounds of sulphur (from stoves and putrefaction). From what has been said it will be understood that air expired in human respiration is less pure than the ordinary fresh air, because it contains some of the waste products of the body. It will, therefore be convenient to state the broad differences between fresh and expired air in a table :

It should be added that expired air as well as containing less oxygen and very much more CO2, also contains more organic matter and more water than fresh air. The burning of fires, gas and candles also makes fresh air less pure, for the CO, and sulphur are both increased, and fine particles of carbon are also added. It may be noted that

a single gas burner spoils as much air as two men. It is these changes which constitute the injury to the atmosphere of a smoke nuisance. Decomposition of animal or vegetable matter and dust also pollute the air.

Further, the atmosphere contains a good deal of solid matter as fine particles. These consist of organic or inorganic dust, carbon particles, bacteria, and so forth. Their origin is due to dirt in towns, to uncleanliness in houses, to trade processes, and to the various pollutions to which reference has been made. Such particulate pollution depends also upon dryness of the air and absence of rain, upon gravity, upon season and aircurrents, and upon the general surroundings of town or country.* The atmosphere of towns and of stuffy rooms and ill-ventilated workshops is more contaminated in every way than sea air or fresh country air. The usual index of polluted atmosphere is the degree of carbonic acid present.

Some Physical Properties of Air.

Before we consider what can be done to provide fresh air in the home and the workshop it is necessary to remember some of the physical properties of air. Three of them may be stated thus :

I.

2.

Air can be compressed by pressure.

It can be expanded by heat.

3. It can be diffused by both pressure and heat. The volume of air in any given space depends upon the two forces of pressure and of temperature. Indeed, under extreme pressure at a very low temperature, far below freezing, Professor Dewar has

* See Bacteriology and Public Health (Newman), 1904, PP. 73-91.

shown that air can be liquefied. The opposite of compression is also true, air can expand, like other gases, when heated. These forces affect the density of the air, and according to its density it diffuses from one room to another. Now it is upon these three broad facts that ventilation depends. We can force more air into a closed room by pressure, we can expand it by lighting a fire, and we can diffuse it by both forces acting on its density. As cold air has a heavier weight than warm air, it falls and the warm air rises. When we open windows we lower the density in the room, and air, particularly the warm air at the top, escapes. It is thus that we obtain ventilation, or a control of air currents, for that is what ventilation means.

The object of ventilation is to purify the air of houses, workshops, and buildings which have become vitiated by (1) respiration and exhalation of man and animals; (2) the burning of coal, wood, gas, candles, lamps, etc.; (3) decomposition of animal or vegetable substances; (4) pollutions from various trade processes; and (5) household dust and dirt.

The Principles and Methods of Ventilation.

There are, in principle, two chief means of ventilation. The first is what is termed natural, and depends on the character of the inside and outside air currents, the second is known as artificial, and depends on some artifice by which air is propelled into a room or extracted. It is important to remember that the necessity for, and means of, ventilation depend not only upon the chemical composition of air or its physical properties, but other circumstances also. Four of these may be mentioned.