supplied per capita, but comparatively little effort has been made to trace out and bring to light the less evident and often unsuspected factors of contamination, which indicate, or at least should help to determine, the logical method of relief.
The sanitation of the air is a field which has hardly been recognized as such, at least it is not carried on systematically, with that end in view, and the results of present efforts, on the whole, are distinctly behind the progress made in other lines. Indeed, its failure to meet the aggravated needs of our crowded and growing cities can actually be traced on their vital statistics.
The Bearing of Impure Air on Health
An exceptionally clear exposition of the process of breathing is contained in the short essay, 'Air, and its Relation to Vital Energy,' by Professor S. H. Woodbridge, of the Massachusetts Institute of Technology. The oxidation of organic matter within the human body is likened to the process of combustion in a boiler furnace. This analogy applies to every essential point and shows that the conditions making for efficiency in artificial heat production are also those which bear on vital energy. The intensity of combustion within the human body depends upon the rate of exchange between the carbonic acid contained in the venous blood and the oxygen brought into the lungs, or the rapidity at which the waste products brought in from the system are being diluted. A slight abnormal accumulation of this gas in the air cells of the lungs would check this outward leakage or expulsion of waste products and retard regeneration of the blood, but respiration automatically regulates this function. Exhausted air, with deficiency in oxygen and excess of carbonic acid, to sustain equal force, thus requires increased respiration, an unconscious effort, gradually lapsing as the gathering waste products react upon the blood and through it upon vitality. The weakened light of a candle flame in exhausted room air very aptly illustrates also its effect on human beings.
Exhausted Air.—Recent experiments by Fluegge, the eminent German investigator, seemingly contradict this theory. At least they make it appear that the paucity of oxygen and the simultaneous increase of carbonic acid and other waste products, have no appreciable ill effect on the average adult, but that the depression of spirits, headache and drowsiness felt in crowded, ill-ventilated assembly rooms are principally due to disturbance of the thermal functions of the body through heat and moisture. Since these excesses in temperature and humidity always accompany exhaustion they should certainly be regarded as contributory factors, which help to depress the vital powers according to their prominence. It has been asserted, also, that the human organism has long been used to the frequent breathing of foul air, and will