We may, however, by spending much time in poorly ventilated rooms, become so accustomed to the depressing influence of the impoverished atmosphere that we suffer a sort of semi-stupor without being conscious of the fact. How great a wrong is inflicted upon children in the school-room and in the crowded factory, by subjecting them, day after day, for months and years, to a vitiated atmosphere, laden with the poisonous exhalations from lungs and skin! Their growing bodies are stunted and their awakening intellects dulled, and the seeds of disease and weakness are implanted to develop into a harvest of wretchedness and misery in later life. =Sea Air.=--When the breeze is off the ocean, the air is practically free from the exhalations of animals, the smoke and soot of chimneys, and the gases of sewers. The curative value of sea-air is well known. It comes richly laden with ozone, and its effect upon sojourners at the sea-side is very stimulating. Many persons are not strong enough to endure sea-bathing, yet gain much benefit from the sea-air. =Mountain Air.=--The air of the mountains is pure. It is usually still, and seldom foggy. Being more rarefied than that of the low-lying valleys, it contains less oxygen in proportion to volume, but its lesser density gives to the oxygen greater activity. The body loses heat less rapidly in rarefied atmospheres, so that there is probably less need of heat-production on the mountain than on the plain, combustion being less active. The rapid and great variations of temperature of the mountain regions stimulate the vital processes and contribute to the curative agencies of those altitudes. =Night Air.=--There is a prevailing prejudice against night air. By many persons out-door air is shut out of the sleeping room as if it were pestilential. Analysis as well as experience shows that the most vitiated and unwholesome night air is that which has been breathed over and over again in a close sleeping apartment. Admit the outside air freely if you desire health. Guard against draughts, and use just enough bed covering for comfort. =Air of the School-Room.=--A plentiful supply of pure air is desirable wherever there are people to breathe it. In no place is it more important than in the school-room. Confined for six hours each day during the period of life when the best health conditions are required for the proper growth of mind and body, the child thus robbed of the needed oxygen is wronged. The adult who voluntarily subjects himself once or twice a week for two hours to the poisonous atmosphere of church, lecture hall, or theatre, may experience a temporary headache, but is soon revived after reaching the fresh air. The child, ignorant of the wrong he is made to suffer, and incapable of providing better conditions, breathes the poisonous exhalations from fifty pairs of lungs, day after day, and thus has sown in his system the seeds of disease.