The average individual breathes in and out about eighteen times a minute, taking into his lungs the air surrounding him at the time and expelling air so modified as to contain large amounts of carbonic acid, organic vapor, and other waste products of the lungs. The volume of air taken in is about the same quantity as that expelled and amounts to eighteen cubic feet per hour. Fortunately, the air expired at a breath is at once rapidly diffused throughout the surrounding atmosphere, so that, even if no fresh air were introduced, the second breath inhaled would not be very different from the first. But after a certain length of time the air becomes so saturated with the waste products of the lungs that it is no longer fit to breathe, and it is evident that in order to keep the air in a room so that it can be taken into the lungs with any reasonable degree of comfort, there must be a continual supply of fresh air admitted with a proper provision for discharging polluted air. If this is not done, there is, so far as the lungs are concerned, a process established similar to that which is occasionally found when a village takes its water-supply from a pond and discharges its sewage into the same pond.

Not long ago, the writer found in the Adirondacks a hotel built on the side of a small lake which pumped its water-supply from the lake, and discharged its sewage into the same lake only a few feet away from the water intake. That the hotel had a reputation of being unhealthy, and that it had difficulty in filling its guest rooms, is not to be wondered at, and yet individuals will treat their lungs exactly as the hotel treated its patrons.

Effects of bad air.

In order to establish a proper relation between the amount of impurities diffused through the air and the physiological effect on individuals breathing that air, certain observations have been noted and certain experiments have been made which prove without question the injurious effect of vitiated air.

Professor Jacob, late Professor of Pathology, Yorkshire College, Leeds, gives the following example on a large scale, to show the results of insufficient ventilation: "A great politician was expected to make an important speech. As there was no room of sufficient dimensions available in the town, a large courtyard, surrounded with buildings, was temporarily roofed over, some space being left under the eaves for ventilation. Long before the appointed time several thousand people assembled, and in due course the meeting began; but before the speaker got well into his subject, there arose from the vast multitude a cry for air, numbers of people were fainting, and every one felt oppressed and well-nigh stifled. It was only after some active persons had climbed on the roof and forcibly torn off the boards for a space about twenty feet square that the business of the meeting could be resumed."

Remembering that the process of breathing is for the purpose of supplying oxygen to the blood and that the absorption of oxygen in the lungs is the same process which goes on when a candle burns, the following experiments were made by Professor King of the University of Wisconsin, to show the effect of expired air on a candle flame. He took a two-quart mason jar and lowered a lighted candle to the bottom, noting that the candle burned with scarcely diminished intensity. Through a rubber tube, he breathed gently into the bottom of the jar, with the result that the candle gradually had a reduced flame and was finally extinguished. He observed also that if the candle were raised as the flame showed signs of going out, the brilliancy of the flame was restored, while lowering the candle tended to extinguish the flame. Even when the candle was raised to the top of the jar, the flame was extinguished after sufficient air had been breathed into the jar. Clearly, then, he argued, air once breathed is not suitable for respiration, unless much diluted with pure air. He argued from this that if a candle using oxygen for combustion could not burn in expired air, therefore an individual using oxygen for the renewal of the blood could not be properly supplied in a room partially saturated with the expired products of the lungs.

Professor King also experimented with a candle burning in a jar on which the cover had been placed, and found that the candle was extinguished in thirty seconds, and he argued that if a candle was thus extinguished on account of the carbonic acid given off, so a person shut up in an air-tight chamber would similarly be extinguished in the course of time.

To prove that expired air is poisonous to animal life, Professor King experimented on a hen, placing the same in a cylindrical metal air-tight chamber eighteen inches in diameter and twenty inches deep. The hen became severely distressed for want of ventilation and died at the end of four hours and seventeen minutes.

In the Wisconsin Agricultural Experimental Station, an experiment was conducted for fourteen days on the effect of ample and deficient ventilation on a herd of cows. The stable was chiefly underground and had two large ventilators which could be opened or closed at will. The food eaten, the water drunk, the milk produced, and weight of the cows were recorded each day. For a part of the time the cows were kept continuously in the stable with all openings closed, and then the ventilators were opened, the alternate conditions being repeated at intervals of four days. The amount of food consumed was practically the same under both conditions. The quantity of milk given was greater with good ventilation. The chief difference was in the amount of water consumed, since with the insufficient ventilation the cows drank on the average 11.4 pounds more water each, daily, and yet lost in weight 10.7 pounds at the end of each two-day period. Examination of the animals themselves also showed that a rash had developed on their bodies which could be felt by the hand and which was apparently very irritating, since it was so rubbed by the animals as to cause the surface to bleed. The evident teaching of the experiment is that under conditions of poor ventilation, it was impossible for the lungs to remove waste products to as great an extent as usual, and, therefore, the demand for additional water was felt in order to stimulate greater action on the part of the kidneys to care for these waste products. That this was not a successful substitute was shown by the loss of weight in the animals, and by the irritation of the skin which evidently was trying to eliminate some of the remaining impurities through its surface.

Modifying circumstances.

Fortunately for mankind, it has not been customary, nor even possible, to build dwellings or stables approaching the air-tightness of a fruit jar. Air has great power of penetration, particularly when in motion, and a wind will blow air through wooden walls, and even through brick walls, in considerable quantity. It is practically impossible to build window casings and door frames so that cracks do not exist, through which air may find its way. When, however, in the wintertime, storm windows have been put on, or when, as occasionally happens, to keep out drafts, strips of paper are pasted carefully around all window casings, or when rubber weather strips are nailed tight against the windows and doors, conditions are obtained which resemble the mason fruit jar, and under those conditions, a person living continuously in such a room is experimenting on himself as Professor King did with the candle.

Another reason why it is difficult to make a room an air-tight chamber is that if a stove or fire-place be in the room, a strong suction is produced through the flame, and such suction requires the entrance of outside air. It is a common experience that a fire-place in a room otherwise tight will refuse to draw and will smoke persistently until a door or window is opened, when, a supply of air being provided, the fire is made bright and active.

Fortunately, the vitiation of the air in a room is never so severe as that in an experimental chamber, and there are few examples which can be cited of men or women dying from lack of ventilation in an ordinary room. But the serious aspect of inadequate ventilation is not that it actually induces death, but that it decreases the powers and activities of the various organs of the body; that it interferes with their normal processes, that it loads up in the body an accumulation of organic matter which is normally oxidized by fresh air and which, if not oxidized, obstructs the activities of other organs of the body.

Danger of polluted air.

Unfortunately, it is not possible to detect by the physical senses that point at which the human organism suffers from insufficient ventilation. Some years ago, Dr. Angus Smith built an air-tight chamber or box in which he allowed himself to be shut up for various lengths of time in order to analyze his own sensations on breathing vitiated air. He found that, far from being disagreeable, the sensation was pleasurable, and he says, "There was unusual delight in the mere act of breathing," although he had remained in the chamber nearly two hours. On another occasion he stayed in more than two hours without apparent discomfort, although after opening the door, persons entering from the outside found the atmosphere intolerable. He placed candles in the box, which were extinguished in a hundred and fifty minutes, and a young lady, who was interested in the experiment, going into the box as the candles went out, breathed it for five minutes easily; she then became white, and could not come out without help.

Nor is it possible to conclude from the experiments and observations cited that the body remains indifferent to polluted air until the latter has reached a certain definite saturated condition. There can be little doubt but that a degree of pollution far short of that necessary to produce death has a weakening effect on the human organism, and that by means of the increased functional activity of other organs doing work intended for the lungs the resistance to disease is much impaired. Life is a continual struggle of the bodily tissues against the attacks of the micro-organisms and their tendencies to destroy life; hence inadequate ventilation or any other condition which interferes with the normal action of the organs of the body causes weakness and affords opportunity for the attack of some disease-producing germ. It stands to reason that an individual whose lung tissues have become soft and incapacitated must be more liable to succumb to disease than another whose lung capacity is large and whose blood has been continually and sufficiently oxygenated.

Perhaps no more impressive proof of this is seen than in the ravages of consumption, which is so prone to attack those whose vitality is diminished by living in unhealthy and unventilated cellars or in crowded tenements. Statistics are very definite on the subject of tuberculosis among Indians, who rarely suffer from the disease when living in tents or on the open prairie, but when they become semi-civilized and crowd together in houses heated through the winter months by stoves, the germs of tuberculosis take firm hold, and the deaths from this disease are greater in proportion to population among this race than anywhere else.

Effect of change in air.

This discussion illustrates another law of disease which makes the necessity for ventilation particularly great among rural communities where for nine months in the year outdoor life is freely enjoyed, namely, that when either an individual or people are brought under changed conditions, perhaps not unwholesome to those accustomed to them, those unaccustomed will suffer severely. So a lack of ventilation during the winter months in a farmhouse is very serious in its consequences to those who have had the full enjoyment of fresh air through the rest of the year.

Reference has already been made (in Chapter 1) to the prevalence of influenza in rural communities, and it is quite probable that this would be largely eliminated if the lungs were not deprived of their oxygen as they are in most houses on the farm.

Composition of air.

Ordinary air contains about 0.04 per cent of carbon dioxid; that is, four parts in ten thousand parts of air, the other nine thousand nine hundred ninety-six being made up of oxygen and nitrogen. Of course, it is not possible to express any definite value for the amount of carbon dioxid which is objectionable in air, because, in the first place, it is not certain that the carbon dioxid in itself is the cause of diminished vitality due to insufficient ventilation, and, in the next place, insufficient ventilation affects different people in different ways. But it is known that in the lungs the life-giving oxygen is changed to carbon dioxid, and that just as carbon dioxid gas will prevent the combustion of a candle flame, so carbon dioxid gas will destroy the life of man.

When a deep well is to be cleaned out, the decomposition of organic matter in the bottom of the well will have, in all probability, caused the formation of this same carbon dioxid gas, and it is not uncommon for a man descending into such a well to be overcome by the gas, which, in some cases, even causes death. For this reason, it is common to lower into a well, before it is entered by a man, a candle or lantern, on the probability that if the lantern can stand it, certainly the man can, while if the lantern goes out, it is wise to avoid the risk of having a man's life put out in the same way.

Organic matter in air.

The stuffy and close feeling perceived in an ill-ventilated room is, however, due to the organic matter from the lungs, which is expired along with the carbon dioxid, and some chemists have argued that this amount of organic vapor ought to be measured instead of the carbon dioxid.

At the present time there is no simple and direct method of measuring organic vapor, and because this vapor increases in the atmosphere proportionately to the carbon dioxid gas, it is much simpler to measure the latter. Then it is impossible to fix a standard of carbon dioxid because a person whose lungs are well developed and whose blood is well oxygenated, or, as we say, one who has good red blood can stand, even if uncomfortable, a few hours of a bad atmosphere without suffering serious discomfort, while an anÆmic or poor-blooded person would be affected to a greater degree. It is for this reason that in any house no living room, especially one heated by a coal stove, should be shut up tight against fresh air. This is the reason why the women of the family, who have to breathe the same air over and over all day, are pale and weak and easily susceptible to disease, while the men, who are out of doors most of the time, and when indoors are made restless by the bad air, suffer much less from the ill effects.

Experiments seem to show that when the amount of carbon dioxid in the air has doubled, that is, when the expired air mixed with the air in the room has increased the proportion of carbon acid from four parts in ten thousand to eight parts in ten thousand, that the air is seriously affected, and that such ventilation ought to be provided that no greater amount than this could occur. This is such a condition that the room smells "close" or stuffy to a person coming in from outdoors, indicating organic emanations as well as an excess of carbonic acid gas. The question then is: how may this condition be avoided in an ordinary house, or in an ordinary stable, because the health of the cattle on a farm, judging at least by the character of the buildings provided, is quite as important as the health of the farmer's family.

We must take it for granted that no such elaborate schemes are possible as in public buildings or schools, where fans are provided, either to force air into the several rooms or else to suck it out. The ventilation of the house must be more simple and easily adjusted and must depend on the principle of physics that warm air rises and that if the warm air of a room is to be removed, air must in some way be supplied to take its place. The two essentials for ventilation are opportunity for the ingress and the egress of air—ingress for fresh air and egress for polluted air.

Fresh-air inlet.

In the construction, of a dwelling house, special and adequate preparation for the admission of fresh air is seldom provided, so that the existing openings must be used for the purpose. This means that in the summertime an open window will furnish all the fresh air which a room receives and, when the temperature of the outside air is approximately that of the living room, such provision is ample and satisfactory. But in the wintertime, when the outside air is cold, the average person will prefer to suffer from the bad effects of impure air rather than admit cold air which may cause an unpleasant draft.

One of the simplest and best methods of providing an inlet for fresh air, without at the same time allowing blasts of wind to enter the room, is to fasten in front of the lower part of the window a board which shall just fill the window opening; then, raising the lower sash a few inches will allow fresh air to enter both at the bottom, where the board is placed, and at the middle of the window between the sashes (see Fig. 14). Persons sitting close by a window thus arranged may feel a draft even under these conditions, since the cold air thus admitted will sink at once to the floor and then gradually rise through the room to the ceiling, but unless one sits too near the window, this is an admirable method of admitting fresh air.

Another method, where steam or hot-water radiators are placed in the room, is to connect the outer air, either through the lower part of the window or through the wall of the room just below the window opening, with a space back of the radiator, so that the cold air entering will pass around and through the radiator and so be warmed as it enters.

The picture (Fig. 15, after Jacobs) shows the arrangement of the radiators in one of the buildings of the University of Pennsylvania. A is the opening in the wall below the window; D is a valve which regulates the amount of air entering through the opening; R is the radiator; B is a tin-lined box which surrounds the radiator; T is a door in front of the box, which when raised allows the air of the room to be heated and to circulate through the radiator. By adjusting the two valves D and T, air of any desired temperature can usually be obtained. Figure 16 (after Billings) shows an English device intended for the same purpose. The valve D in this case operates to admit air, either through the radiator or to the space between the radiator and the wall, in order to vary the temperature of the entering air. The valve T may be open or closed, and its position, together with that of the valve F, determines the proportion of the room air which is reheated.

The writer remembers one schoolhouse where these methods were used successfully, the radiators being placed directly in front of the window and inclosed at the back, sides, and top, except for an opening to the outer air through the wall, properly controlled by a damper. In the writer's own office the radiators are by the side of the window and are boxed in, the connection being made with the outside air through a wooden box entering under the radiator. This is an admirable method, provided the radiator has sufficient surface to warm the fresh air admitted.

Another excellent arrangement is to provide a narrow screen similar to that used for protection against flies, but with the screening material of muslin cloth instead of wire cloth. This muslin will break up the current of air so completely that no draft is felt by persons sitting even close to the open window.

Position of inlet.

The inlet for fresh air, if connecting directly with the outside air, should not be at the top of the room, since then the inlet would not serve to admit air, but rather to allow the warm air of the room to escape, and a burning match would inevitably show a draft outward instead of inward.

Neither is it desirable to have the fresh-air inlet near the floor of the room unless the entering air is warm, because cold air admitted will flow across the floor and remain there, not disturbing the warm upper layers. The effect then is not to improve the ventilation, but only to chill the feet of persons sitting in the room. The position of the window lends itself, therefore, to admission of fresh air, since it is neither at the top nor at the bottom of the room, but at the level most suitable for such admission.

Foul-air outlet.

Very few houses have any provision for the outlet of spent air, and if ventilation is thought of at all, the only idea usually is to provide, in part at least, for the admission of air and to make no adequate arrangement for its egress. Whenever a stove or fire-place is in use, the mere burning of fuel requires the consumption of air, and in cases where apparently no air is admitted to the room, insensible ventilation is at work bringing into the room, through the walls and through cracks around the doors and windows, the necessary air for combustion.

It may be proved by the laws of physics that a coal stove burning freely in a room causes adequate ventilation; and that only where the dampers of the stove are closed, so that not merely is the supply of fresh air diminished, but also the products of combustion are thrown out into the room, is there danger from lack of ventilation. The stovepipe in this case furnishes the necessary outlet for the impure air, and the following suggestion has been made in order to utilize this outlet, even when the fire is not burning freely or when the damper in the stovepipe is closed. If the stovepipe from a stove is carried horizontally, as it usually is, an elbow must be provided to raise the pipe to the stove hole in the chimney. Then providing a T connection at the point marked A in Fig. 17 (after Billings), the lower part of the T may be carried to within a foot of the floor with a damper at the points B and C. When the fire is burning freely, the damper at C is closed, and ventilation is secured through the stove, the damper at B being open. When the damper at B is closed and the fire checked, then the damper at C may be opened and the impure air drawn up the chimney from the level of the floor. This, it is said, is an effective arrangement for drawing off the polluted air of a room.

Another method is to surround the stove with a sheet-iron casing, as shown in Fig. 18 (after Billings), the top of the casing having a pipe leading into the chimney independently from the stovepipe. The casing becomes warm and heats the room by radiation, just as the stove does, but if the damper in the flue from the casing be opened partly, a strong draft along the floor and into this casing will be developed and the foul air thereby discharged into the chimney. It will be easily possible, of course, to carry away all the heat from the stove in this method, and the damper in the flue of the casing must be carefully regulated to carry away only the desired amount of foul air.

Still another method of using the heat of a stove to secure ventilation is shown in Fig. 19 (after Billings). Here the stove is surrounded with a sheet-iron jacket extending from the floor to about six feet above that level. A pipe is carried from the outside air up through the floor directly under the stove. By regulating the damper in this pipe the supply of fresh warmed air entering the room can be regulated. Doors in the casing must, of course, be provided for the purpose of taking care of the fire, and of allowing air from the room near the floor to be heated instead of the outside air.

A most objectionable method of providing an outlet for polluted air from a room is to have a register in the ceiling with the ostensible purpose of warming the room above. It was the writer's misfortune once to stay a week in the country, in a room over the kitchen where this method of heating was employed, and the odors of cabbage, onions, and codfish which permeated the upper room, and clung there all night, still remain as a most unpleasant memory.

Size of openings for fresh air.

As an indication of the size of the openings needed, it has been said that in order to provide the necessary air movement, and yet to restrict the velocity of the moving air so that no objectionable drafts will be experienced, at least twenty-four square inches sectional area should be allowed as an inlet for each person, so that one square foot is required for six persons. This is, perhaps, a theoretical requirement. Certainly, it is more area than is likely to be obtained in actual ventilation. The space between two windows, for instance, is about one inch by thirty inches,—barely enough, according to this rule, for one person, and yet that opening is sufficient to appreciably improve the quality of the air in a room occupied by three or four persons.

Taking into account the necessary air required by lamps or gas burners, the inlet flue should have at least ten square inches area for each person, so that the ordinary single register should provide the necessary amount of air for a living room. When, as happens in houses where a studied effort is made to preserve the health of the inhabitants, an outlet is cut into the wall and a flue carried up through the roof, the flue should be preferably near the floor and on the side of the room opposite the window or inlet. With such an arrangement (see Fig. 20) the air entering rises at first, but sinks at once because of the temperature, so that the direction of the air currents are diagonally across the room from the ceiling to the floor, thus renewing and changing all the air particles except those directly over the outlet. Where the air is introduced mechanically, that is, forced into the room, it is better to have the inlet and outlet on the same side, so that the entering air is shot in at the top, flowing across the room, then sinking and coming back, just below the point where it entered.

Ventilation of stables.

All that has been said on the subject of ventilation in houses applies equally well to the ventilation of stables, and a little book by Professor King of the University of Wisconsin, entitled "Ventilation," deals most thoroughly with the principles and practices of ventilation, not merely for dwellings but also for stables. Professor King proves by his experiments that the condition of cattle is much improved and that the milk-giving qualities are increased by a proper supply of fresh air, and in the book referred to, he gives a number of examples of the proper construction to provide adequate ventilation. It is most convincing to see how unscientific is the old-fashioned underground stable, the sole idea of which was to conserve the animal heat by crowding together the cows and by absolutely excluding the outside air. For further details of his work, its principles and practices, the reader is referred to the book, which may be obtained from the author at Madison, Wisconsin.

Cost of ventilation.

To ventilate a house is expensive, and to ventilate a barn requires not only a certain expenditure of money but also a considerable amount of judgment. It is evidently cheaper to heat the same air in a room over and over than to be continually admitting cold fresh air, which will have to be warmed. This extra cost is, however, not excessive, when the movement of the air currents is properly controlled. The cost of warming the air necessary for ventilation for five persons should not be, at the rate of 1000 cubic feet of air to each person, more than ten cents a day in zero weather, with coal at five dollars a ton. Enough coal will have to be burned in addition to compensate for radiation, or, in other words, it requires a certain amount of coal to keep an empty room warm in winter without any question of ventilation, and in some badly built houses this amount is large.

Relation of heating to ventilation.

It does not follow because much heat is lost in this way that the ventilation is good, since the heated air may ascend to the ceiling and there escape without influencing the ventilation. In fact, one of the first principles of ventilation is that as soon as regular inlets and outlets are provided, all other openings ought to be rigidly closed. Then and then only can the warmed pure air be admitted as desired, at the points intended, and the full value of the heat utilized. Especially is this control of openings important in ventilating barns. Here each animal is a natural heater, warming the air by direct contact and by rapidly breathing in and out large volumes of air which are thereby changed to a temperature of over ninety degrees Fahrenheit. The air around their bodies being warmed rises to the ceiling and spreads out to the two sides and is there gradually cooled and at the same time mixed with fresh air which enters at the top, so that the cow is constantly supplied with freshened air. A flue is needed to carry the foul air up through the roof, and fresh-air inlets in the outer walls on both sides are required, and with these openings carefully controlled and with no others interfering, the stable may be well ventilated, as shown in Fig. 21 (after King).

In all cases where ventilation is to be practiced, the walls and ceiling should not merely be tight in themselves, but they should be double, and the strictest attention paid to limiting the amount of heat lost by radiation. All the heat used ought to be concerned in ventilation, and in that only. To secure air-tight walls and ceiling, the studding and joists should be boarded in, both on the inside and out, and the space between should be filled with shavings, straw, dry moss, or any similar fibrous substance. The outside sheathing must be well laid and must be water-tight in order that rain shall not penetrate to the inside of the wall, and the roof must be tight so that the ceiling filling does not get wet and rot.

The choice, therefore, so far as ventilation of either house or barn goes, lies between a poorly built, loose-jointed structure without artificial ventilation and with poor economy in heat, and a well-built, air-tight structure, with ample ventilating pipes, carefully and intelligently planned and built. The first is healthy so far as pure air is concerned, but drafty and uncomfortable. The second is more expensive to build, but insures lasting health and comfort. Then the choice cannot but fall on the building which is easy to warm, healthful to live in, and readily ventilated.