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the body as fast as the blood conducts it to the but dry air at the same temperature is pleasant and e. On the other hand, moist air at 6o0 F. is not ant provided it is unmixed with the organic matters eath, but moist air at 750 or 8o0 F. is very enervating ng. The reason is that moist air not only conducts this temperature, but causes the vapours evaporating e skin to be condensed upon its surface without being removed, giving rise to a hot and oppressive feeling, the walls of a building are cold, some of the moisture e breath of the audience condenses upon them, and e floating dust particles cooled by the air which comes ct with the walls. These dust particles so moistened the bacteria into rapid and astounding vitality, because .1rganic matters evolved in breath are excellent bacteria , the result being that active decomposition takes place is manifest to those who enter from the outer air by the and foetid smell. Under these circumstances the body mes heated, and, as the air inhaled cannot carry away moisture fast enough, the feelings experienced are dis. Nature has designed that the latent heat which the ir of water absorbs from the skin shall be the safety reduce the temperature of the body when it exceeds and it is as necessary, therefore, that the air in our 1 public buildijjg^^hould be capable of taking from the human body as
excessive heat and that t> sho
activity of the bacteria in confined air spaces, and that it is greatest near the point of saturation, especially when that moisture is largely the result of breath exhalation. The circulation of the air against cold surfaces -causes a deposit of water mist, and this aids the bacteria greatly in attacking the organic matters in the air.
A problem of considerable interest to sanitarians has arisen with regard to the organic matters in exhaled air. Some French chemists stated that they had detected toxic poisonous properties in the liquid condensed from breath, but other observers who repeated the experiments afterwards failed to confirm their results. At the present moment there is not sufficient evidence from which to draw definite conclusions, but the subject is as serious as it is important. The fresh liquid condensed from the breath of one individual may be quite free from toxic character, but the condensed products from a moisture-laden atmosphere in which a mixed audience was assembled for a prolonged sitting of three or four hours, and where active decomposition had gone on, would not unlikely give a different result. One thing is certain, that every precaution should be taken to prevent the air in dwelling rooms and public buildings being saturated with aqueous vapour. It is likely that 7o per cent, of saturation is preferable to anything higher, at any temperature, but it will be difficult to keep it as low as this in buildings dependent upon natural ventilation when the temperature of the outside air is near that of the inside air—in other words, when the temperature of the outside air exceeds 550 F.
A point already much debated is as to whether the amount of moisture present in the air which has been heated should be increased in accordance with a rise of temperature, by evaporating water where the heating is being effected. If the outside atmosphere is below 320 F., and it has been below that temperature for some time, it is advisable to add moisture artificially, when the air is being raised to 6o0 or more, and this is so whatever method of heating is adopted. When steam pipes, at a high temperature, or stoves are used for heating, it is especially needful that moisture be added to the heated air. It has never been shown satisfactorily why it is that moisture added to air which has been heated over iron plates or pipes should relieve the situation, but there is no question that it does, especially in cases where the products of respiration are known to be absent. Some compounds, carbides or what not, are formed in small quantities, and, whilst in the gaseous state, exercise a deleterious effect, but combine probably with the moisture added to the heated air, and lose their baneful properties. No such unpleasant feelings are experienced in air heated over hot water pipes which do not exceed 15oo F., and, from professional experience, the author has no hesitation in saying that the addition of moisture need not be a matter of anxiety. It has been urged that moisture should be added to heated air so as to raise the moisture to 75 per cent, of saturation. There is no doubt that moisture should be added to air heated over stoves, hot iron plates and steam pipes, and it is best to make a point of doing this by providing tins to contain water which can be evaporised by the heat employed. Where hot water is used for heating, there is no necessity to do this when the temperature of the air outside exceeds 45o F. In the majority of public buildings, the same air, unfortunately, is continually circulating around the heating appliances, and the breath of the audience is reheated over and over again. So large a proportion of moisture is obtained from this source, that it is most unwise, with the present provisions for the introduction of fresh air at the floor level, to add more moisture, because it must not be forgotten that the larger the proportion of moisture present, the more rapidly are the matters evolved in breath acted upon by the bacteria, and the more rapidly, too, are iron carbides and unpleasant products formed by heated iron plates and strongly heated iron surfaces. It will be time enough to deal with the addition of moisture to the air heated in churches and public buildings when the serious deficiency of fresh air introduced at the ground level has been remedied. Where, as now for the most part, air falls from the roof, and mixing with the breath of the audience, circulates through the heater or around the hot pipes, enough moisture is present. In the few instances where proper inlet provision is made, and the temperature of the air outside is below 450, a little moisture will certainly tend to remove the feeling of dryness which the skin assumes, and the irritation of the eyes which results when dry air has been heated over very hot surfaces.
Hospital wards should only be heated by air which has passed over hot water pipes whose temperature never exceeds 17oo or 18oo F. If this is done I think that no moisture should be added except during very cold weather, because a dry atmosphere is more exhilarating, and one in which the germs are rendered powerless to do much mischief.
When air is moderately dry there is no fear of moisture being condensed upon the walls and cool surfaces of wards and rooms where persons are gathered who evolve sputae, or other germs of infectious disease. The oxidation of the food products in the lungs and blood appears to proceed more readily and easily when the air, which is heated to a higher temperature by being inhaled, carries off a not considerable proportion of moisture from the lungs. From experiments carried out in the House of Commons with a view to reduce the temperature of the inlet air during the summer, it was found that although it was only lowered one or two degrees by passing over blocks of ice there was a " sensation of freshness" produced in excess of what seemed probable under the circumstances, and this was due doubtless to the condensation of some of the moisture present.
Much might be said for and against the washing and filtering of air in order to remove impurities. Some of the leading scientists are in favour of such a proceeding. The addition of further moisture which results in winter previous to the air being heated is not of much consequence when the temperature of the air outside is below 5o0 F., but if it is above this, and especially in summer when the air is humid, it is not at all wise to increase the moisture present. In summer, therefore, if the washing process is done with a small quantity of water which is nearly as warm as the air, the result will be unsatisfactory and better left alone.
It is a point difficult to determine, perhaps, but a debatable question notwithstanding, whether it is advisable to remove the soot and such like antiseptic matter from the air by washing and filtering as is done in some large buildings. If a large quantity of water can be used in summer and it is cool enough to lower the temperature of the inlet air by several degrees, then by all means do it because it is unlikely that much more moisture will be taken up. In winter, unless the washing can be done thoroughly, it is better not attempted in clear weather as the antiseptic and germ killing ingredients are the first and easiest removed whilst other and more deleterious matters pass the screen. Furthermore, the value of the alkaline ingredients accompanying the tarry products in maintaining the lungs in a vigorous condition is a point which has not been duly considered.
Where such lengthy sittings occur as in the House of Commons, for instance, the air driven in should be purified from fog, but air which has been washed and filtered without having its temperature lowered is soft and enervating, lacking freshness and invigorating power.
It is impossible to heat by stoves, or to pass air over iron plates heated by a furnace without some carbonic oxide passing outwards into the air, and, where the conditions prevent this, the organic matters in the air, and especially those in breath exhalations, give rise to the compound. Various iron and other products are also generated, and these are so