The air as expelled from the lungs contains, not only a certain amount of organic matter in the form of vapor, but minute solid particles of debris and bacterial micro-organisms (Chap.  XIV).  The air thus already vitiated, after it leaves the mouth, putrefies very rapidly.  It is at once absorbed by clothing, curtains, carpets, porous walls, and by many other objects.  It is difficult to dislodge these enemies of health even by free ventilation.  The close and disagreeable odor of a filthy or overcrowded room is due to these organic exhalations from the lungs, the skin, and the unclean clothing of the occupants.

The necessity of having a proper supply of fresh air in enclosed places, and the need of removal of impure air are thus evident.  If a man were shut up in a tightly sealed room containing 425 cubic feet of air, he would be found dead or nearly so at the end of twenty-four hours.  Long before this time he would have suffered from nausea, headache, dizziness, and other proofs of blood-poisoning.  These symptoms are often felt by those who are confined for an hour or more in a room where the atmosphere has been polluted by a crowd of people.  The unpleasant effects rapidly disappear on breathing fresh air.

219.  The Effect on the Health of Breathing Foul Air.  People are often compelled to remain indoors for many hours, day after day, in shops, factories, or offices, breathing air perhaps only slightly vitiated, but still recognized as “stuffy.”  Such persons often suffer from ill health.  The exact form of the disturbance of health depends much upon the hereditary proclivity and physical make-up of the individual.  Loss of appetite, dull headache, fretfulness, persistent weariness, despondency, followed by a general weakness and an impoverished state of blood, often result.

Persons in this lowered state of health are much more prone to surfer from colds, catarrhs, bronchitis, and pneumonia than if they were living in the open air, or breathing only pure air.  Thus, in the Crimean War, the soldiers who lived in tents in the coldest weather were far more free from colds and lung troubles than those who lived in tight and ill-ventilated huts.  In the early fall when typhoid fever is prevalent, the grounds of large hospitals are dotted with canvas tents, in which patients suffering from this fever do much better than in the wards.

This tendency to inflammatory diseases of the air passages is aggravated by the overheated and overdried condition of the air in the room occupied.  This may result from burning gas, from overheated furnaces and stoves, hot-water pipes, and other causes.  Serious lung diseases, such as consumption, are more common among those who live in damp, overcrowded, or poorly ventilated homes.

220.  The Danger from Pulmonary Infection.  The germ of pulmonary consumption, known as the bacillus tuberculosis, is contained in the breath and the sputa from the lungs of its victims.  It is not difficult to understand how these bacilli may be conveyed through the air from the lungs of the sick to those of apparently healthy people.  Such persons may, however, be predisposed, either constitutionally or by defective hygienic surroundings, to fall victims to this dreaded disease.  Overcrowding, poor ventilation, and dampness all tend to increase the risk of pulmonary infection.