I have hitherto referred only to the dispersion of poisonous exhalations, as if the best and most necessary thing the atmosphere can do for us were to dilute the dose to a comparatively harmless potency. But this is now known to be not the true remedial process with respect to the zymotic germs. The most wonderful achievement of recent investigation reveals a philosophy of both bane and antidote that astonishes us with its simplicity as much as with its efficiency. At the moment when humanity stands aghast at the announcement that germs are not destroyed by disinfectants, comes the counter discovery that they are rendered harmless by oxygen. It seems that it makes no difference, really, of what sort or from what source are the bacteria that we take into the blood. The only material difference to us depends on the sort of atmosphere in which their hourly generations are bred. For example, the bacteria developed in confined air, from a simple infusion of hay, are found by experiment to be as capable of generating that most terrible of blood poisoners, the malignant pustule, as are the bacteria taken from the pustule itself.
On the other hand, the bacteria from the malignant pustule itself, after propagating for a few hours in pure and free air, become a perfectly harmless race, and are actually injected into the blood with impunity. The explanation of the strange discovery is this—note its extreme simplicity—bacteria bred in copious oxygen perish for want of it as soon as they enter the blood vessels; whereas those inured to an unventilated atmosphere for a few generations, which means only a few hours, are prepared to thrive and propagate infinitely within our veins; and that is the whole mystery of blood poisoning and zymotic diseases. Taken in connection with the narcotic or nerve-poisoning power of carbonic acid (to which all the classes of diseases resulting from colds are due), we have also in this simple but grand discovery the whole mystery of the question with which we set out—why free air is health, and why sickness is a purely domestic product. The restitution of natural health to mankind demands only, but demands absolutely, the constant diffusion in copious and continuous floods of atmospheric oxygen, of the nerve-poisoning carbonic acid of combustion (organic and inorganic), and of the blood-poisoning bacteria of organic decomposition.
We find, then, as a matter both of experience and of philosophy, that life or death, in the main and in the long run, turns on the single pivot of atmospheric movement or obstruction. The resistance of mere rising ground or dense vegetation to a free movement of the air from low-lying levels performs an obstructive office similar to that of the walls and roofs of houses, and with like effect. The invariable condition of unhealthy seasons and days is a state of rarefaction and stagnation of the atmosphere, when the poison-freighted vapor cannot be lifted and dispersed, and every one complains of the sultry, close, "muggy" (meaning murky) feeling of the air. Few reflect, when fretted by the boisterous winds of March, upon the vital office they perform in dispersing and sanitating the bacteria-laden exhalations let loose by the first warmth from the soaked soil and the macerated deposits of the former year.
The passing air, then, that we breathe so lightly, is on other business, and carries a load we little think of, and that is not to be trifled with. This grand carrier of nature, on business of life or death, must not be detained, must not be hindered! or they who interfere with the business by restraining walls and roofs will take the consequences. It is a good deal like stopping a bullet, except as to consciousness and suddenness of effect.
That men live at all in their obstructed and therefore poison-loaded atmosphere, is a proof of the wonderful efficiency of the protective economy of Nature within us; so wonderful, indeed, that few can believe the fact of living to be consistent with the real existence of such a deadly environment as science pretends to reveal. It is a common impression, therefore, that actual results fail to justify the alarm sounded by sanitarians. Hence the necessity for calling attention at the outset to an ample and manifest equivalent for the deadly dose of confined exhalations taken daily by all civilized men. We perceive that that dose is not lost, like the Humboldt River, in a "sink," but reappears, like the wide-sown grass, in a perennial and universal crop of diseases, almost numberless and ever increasing in number, peculiar to house-dwellers. The trail of these plagues stops nowhere else; it leads straight to the imprisoned atmosphere in our artificial inclosures, and there it ends. That marvelous protective economy of Nature within us, to which we have referred, is no perpetual guaranty against the consequences of our negligence; it is only a limited reprieve, to afford space for repentance; and unless we hasten to improve the day of grace, the suspended sentence comes down, upon us at last with force the more accumulated by delay.
Now, therefore, the grand problem of sanitary science (almost untouched, almost unrecognized) proves to be no other and no less than this:
What can be done to remedy the obstructive nature of an inclosure, so that its gaseous contents shall move off, and be replaced by pure air, as freely, as rapidly, and as incessantly, as in the open atmosphere?
It happens to be the most necessary preliminary in approaching this problem, to show how not to do it, for that, respectfully be it spoken, is what we have hitherto practiced, as results abundantly prove. Fallacies, both vulgar and scientific, obstruct our way. A fundamental fallacy respects the very nature of the work, which is supposed to be to get in fresh air. In point of fact, this care is both unnecessary and comparatively useless. Take care of the bad air, and the fresh air will take care of itself. Only make room for it, and you cannot keep it out. On the other hand, unless you first make room for it, you cannot keep it in; pump it in and blow it in as you may, you only blow it through, as the Jordan flows comparatively uncontaminated through the Dead Sea. This is a law of fluids that must be kept in view. The pure air is quite as ready to get out as to get in; while the air loaded with poisonous vapors is as sluggish as a gorged serpent, and will not budge but on compulsion. Such compulsion the grand system of wind suction, actuated by the sun, supplies on the scale of the universe; and this we must imitate and adapt for our more limited purposes.
It would seem as if we need not pause to notice so shallow though common a notion as that which usually comes in right here, namely, that confined air will move off somehow of itself, if you give it liberty; being supposed to be much like a cat in a bag, wanting only a hole to make its escape. Air is ponderable matter—as much so as lead—and equally requires force of some kind to set it or keep it in motion. But applied philosophy itself relies on a fallacious, or, at best, inadequate source of motive power for ventilation. It gravely prescribes ventilating flues and even holes, and promises us that the warmed air within the house will rise through these flues and holes, carrying its impurities away with it, from the pressure of the cooler and denser air without. But we very well know that the best of flues and chimneys will draw only by favor of lively fires or clear weather. They fail us utterly when most needed, in warm and murky weather, when the barometer is low, and the thin atmosphere drops, down its damp and dirty contents, burying us to the chimney tops in a pestilent congregation of vapors.
Nevertheless, so far as I can discover, these holes and flues, at best a little fire at the bottom of the latter, are the sole and all-sufficient expedients of science and architecture for ventilation to this day, in spite of their total failure in experience. I can find nothing in standard treatises or examples from philosophers or architects, beyond a theoretical calculation on so much expansion of air from so many units of heat, and hence so much ascensional force inferred in the ventilating flue—a result which never comes to pass, yet none the less continues to be cheerfully relied on. Unfortunately for the facts, they contradict the philosophy, and are only to be ignored with silent contempt. A French Academician's report on the ventilation of a large public building, lately reprinted by the Smithsonian Institution, states with absolute assurance and exactness the cubic feet of air changed per minute, with the precise volume and velocity of its ascension, by burning a peck of coal at the bottom of the trunk flue. No mention is made of the anemometer or any other gauge of the result asserted, and we are left to the suspicion that it is merely a matter of theoretical inference, as usual; for every one who has had any acquaintance with practical tests in these matters knows that no such movement of air ever takes place under such conditions, unless by exceptional favor of the weather.