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Sources of Impurities in the Atmosphere. The sources of the impurities of the atmosphere may be divided into two classes, gaseous and solid.

Of the gaseous, carbon monoxide and dioxide, marsh gas, hydrogen sulphide, and gaseous organic substances such as ammonia are the most important.

Dust, organic and inorganic, the débris of animal and vegetable organisms, and living micro-organisms constitute the solid form of atmospheric impurities. Among these impurities are included the organic matters from the body, such as epithelium, sweat, the volatile matters from decaying teeth and the digestive tract, and excreta deposited upon unclean clothing.

The impurities due to respiration are the decrease of oxygen, the increase of carbon dioxide, the increase of watery vapor to saturation, and the addition of organic matter. It is said while a large amount of carbon dioxide may escape with very imperfect ventilation, the aqueous vapor and organic matter cling to the surfaces of the room and its contents; the proof of which is the fact that after a prolonged airing an odor of organic matter still remains in such a room.

It is generally conceded that impure air is the most important exciting cause of disease, and that a normal proportion of oxygen in the air is necessary for health, this theory being proven by a well-known fact that among out-of-door workers the death rate is very much lower than among those employed indoors. Pulmonary tuberculosis (phthisis) is especially associated with overcrowding, and the high death rate of jails and barracks, formerly so common, was no doubt due to crowded quarters.

Effects of Bad Air. - The immediate effects of inhaling impure air are discomfort followed by headache, dizziness, and nausea, and if continued, as before stated, with less than 13 per cent oxygen the respiration becomes slow and difficult, perspiration is profuse, and asphyxia and death soon result.

The continued breathing of bad air in lesser quantity causes a gradual loss of health, manifested by pallor, languor, anæmia, loss of appetite, and loss of resistance to diseases, the last being one of the most injurious effects.

The air of workshops and factories contains not only the impurities arising from the respiration and perspiration of men, but to combustion from heating and lighting; and to these may be often added overheating and overcrowding, besides lack of personal cleanli

ness.

Certain occupations expose workmen to impure air from special sources, such as miners, bakers, workers in silk and cotton mills, in bleaching works, in the manufacture of zinc, steel, brass, wall paper, artificial flowers, cutlery, guns, cabinet making, etc.

In factories where hides and feathers are used the dust is of animal origin.

Much attention has been given during recent years to providing sufficient air space and ventilation for workshops and factories, besides apparatus for mechanically removing the dust or fumes arising from the various industries, many states having passed stringent laws for thus protecting workers.

The impurities of the air in dwellings arise from respiration, perspiration, combustion, faulty sewerage, and very largely from bad housekeeping, which permits

uncleanliness of the dwelling and its occupants. With fairly good ventilation the air of a dwelling cannot be pure if it be filled with dusty carpets, curtains, and walls; if both bed and body clothing be soiled, if cellars, pantries, and ice boxes are filled with decaying food and unclean utensils, if bath rooms and kitchen sinks

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FIG. 15. Apparatus for removing dust from the air in manufacturing establishments: a, emery wheel; b, hood over emery wheel; c, exhaust shaft. (Bergey.)

are dirty and drain pipes filled with an accumulation of grease and other filth. It is not too much to say that most dwellings would have better air if there were less furniture and decoration, and more attention paid to everyday cleanliness.

In hospitals the sources of impurities in the air are the same as in dwellings, multiplied by many degrees and to which may be added the manifold germs of disease and exhalations from the bodies of sick persons, thus requir

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ing especial care in guarding against overcrowding and overheating, and in providing perfect cleanliness in every detail of housekeeping and nursing.

In schools and other assembly rooms the impurities of the air are mainly due to overheating and overcrowding, together with the effects of respiration, perspiration, and combustion.

The impure air of large office buildings, courthouses, railway stations, day and sleeping cars is aggravated by the almost universal fault of overheating, which, taken together with the impurities of respiration, combustion, uncleanliness, and faulty ventilation, produce an enormous volume of foul air.

SECTION II

CLIMATE, VENTILATION

The climate of a locality depends mainly upon its distance from the equator, its height above sea level, its nearness to large bodies of water, and its prevailing winds.

Given the same distance from the equator and the sea, a mountain locality will have a cooler climate than a lower level.

The middle of a continent is subject to extremes of heat and cold unknown on the seacoast, while the latter is much more humid.

The prevailing winds are governed by the presence or absence of mountain ranges.

Climate is usually designated as temperate, polar, or tropical.

Climate and Health. In tropical climates disorders of the liver, digestion, and nervous system are common, while in the polar climate the digestion is good, the nervous system sluggish, muscular development greater than in the tropics, but lung and kidney diseases are prevalent.

The temperate climate is therefore the healthiest, as there is less continued strain upon the organs of the body than in the extremes of heat and cold of the tropics and polar regions.

The effects of a tropical climate upon persons coming from a temperate zone are bleaching of the skin, sometimes due to anæmia but generally ascribed to the profuse perspiration, sluggishness, and relaxation, loss of appetite, impaired digestion due principally to drinking too freely to supply the loss of fluids by perspiration, and the common excessive use of alcohol. It is said that the tropical climate acts especially unfavorably upon the female organism.

The infectious diseases, yellow fever, cholera, plague, dysentery, and malaria, prevail in tropical climates. The influence of climate upon certain diseases is well known; that of such regions as the Rocky Mountains, southern California, and the mountains of North Carolina, which are particularly dry, being beneficial to tuberculosis, while the damp cool climate of England and the region of the Great Lakes of the United States is no doubt the cause of the lung and kidney diseases which prevail with alarming frequency during the winter months.

Season exerts a marked influence upon mortality; deaths from diseases of the respiratory system occur

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