Warm moist air is not directly injurious. Chilling on leaving such an atmosphere may occur. When air about So degrees F. becomes saturated, evaporation no longer com pensates for the decreased radiation and heat stroke may follow the rise in body temperature which follows. The effect of this temperature is diminished by light clothing.
Cold damp air is injurious to poorly clad, improperly fed persons either in infancy or old age, or to those having kidney disease, rheumatism, disorders of metabolism or affections of the respiratory passages. Its effect is diminished by proper cloth ing, exercise and an increased diet.
Warm dry air produces the most comfortable sensations and is stimulating. Hot dry air causes an excessive loss of moisture and favors irritation and infection of the respiratory mucosa.
6. The relation of man to air varies in different climates. Thus in the tropics he needs no fire for warmth, no clothing except for modesty and no work to keep warm. The heating and ventilation of the home is of little consequence, since there is little home life. On the other hand in the arctics fires are needed for warmth, while fuel is scarce, and heavy clothing is required to conserve the body heat. As a consequence both heating and ventilation of the home is required. The temperate climate furnishes both of the above extremes during its seasonal variations.
7. Carbon dioxid was formerly considered injurious and also an index of the wholesomeness of air. It is not irritating or poisonous. Its percentage cannot be taken as a guide to the fitness of air for breathing, and we can only employ its determination as a guide to the amount of rebreath ing (vitiation) which has taken place, while it cannot be substituted for the more important determinations of tempera ture, humidity, and motion. Ordinarily it never accumulates in quantities sufficient to cause injury. It is tolerated in quantities up to .ro to .13 per cent.; from 2 to 3 per cent. prod uce increased from 7 to 8 per cent. produce distressing dyspnoea and to to r r per cent. produce headache, nausea and chilliness. Suffocation will occur in an atmosphere of 3o per cent.
8. Heating.—The body must be regarded as a furnace, a
radiator, a thermostat and a humidifier. It not infrequently produces more heat than is needed, whereupon no external heat is required. Less artificial heat is required by young persons, women, and by all persons when exercising. In sedentary life and old age the heat loss is in excess of heat production and then one needs to surround the body with an air blanket of a temperature that in winter will supply heat to the body. The young and active require an air blanket that will absorb heat. Thus a study should be kept warm and a gymnasium cool. Next to the body is a partial blanket of air enmeshed in the hair and clothing, which serves as an insulator. This is present except when a person is exposed to winds. Thinly clad persons, or persons who are poorly nourished, tend to overheat their dwellings, due to insufficient bodily heat production.
Artificial heating as a practice antedates ventilation. At present, especially in large buildings, the two are frequently combined hut it is a difficult matter to secure satisfactory results. Artificial heating is usually with dry air. The capacity of win ter air for moisture is greatly increased after heating, for when cold, even if saturated, it contains relatively little moisture. Artificial humidification is therefore required.
Artificially heat is supplied by various means; (t) by open fire places, (2) by stoves, (3) by hot air furnaces, (4) by the enclosed circulation of steam and hot water, (5) by gas and oil stoves and braziers and (6) by electrical heaters. The first two of these methods usually improve the ventilation of the heated spaces, since the source of the heat is an open flame within the room, which requires a current of air for its active burning, and in order to avoid the smoke the gases are conveyed outside. These currents result in fresh air being drawn into the room from out of doors, Gas and oil stoves vitiate the air, since their gases of combustion are discharged into the room. If maintained in a small room actual danger may arise, due to high concentrations of carbon monoxid accumulating near the floor.