250. Organic Impurities

Organic Impurities. The interior surfaces of the lungs, and the whole exterior surface of the body, exhale moisture continually, although at varying rates. Certain other substances, more or less volatile, are exhaled at the same time. These have a rank odor, especially when abundant, and they decompose very readily, giving rise to odors still more offensive. This class of emanations appear to have a positively toxic or poisonous effect upon those who inhale them. The exact chemical composition of these substances is difficult to determine, but long continued and careful experiments have made it certain that they cause great discomfort and a feeling of oppression, when present in the air in moderate quantities, and that when concentrated they are dangerous.

The quantity of organic substances thus exhaled appears to bear a definite proportion to the amount of carbonic acid produced by respiration in the same time. The ratio is found to be so nearly constant that the percentage of the latter may be safely taken as an index of the quantity of the former existing in the air from the same cause.

There is another large class of organic emanations which pollute the air of dwellings and assembly rooms. These proceed from the bodies of persons who are troubled with indigestion and various gastric and intestinal disorders.

251. The dust found in the air of dwellings, etc., is composed mainly of small fibers derived from the wear and tear of cloth and wood, and minute fragments of various kinds of stone. In thickly populated districts it is likely to contain also soot and the dried remains of decaying vegetable matter. Such dust is, as a rule, comparatively harmless, merely irritating the nostrils and lungs, but doing no positive injury unless it is present in large quantities.

But the dust from wagon roads and paved streets is much filthier in character. A considerable percentage of it consists of finely pulverized horse dung, and in the vicinity of streets paved with stone or asphaltum the greater part of the dust is found to consist of this unsavory material. Wooden pavements are still worse, because they absorb and store up the liquid excreta dropped upon them, giving it off again as dust when dried, and as a most loathsome vapor when wetted by summer showers. Of course such dust as this must be excluded from the lungs at any cost.

252. There is another ingredient occasionally found in dust which deserves close attention, that is, the germs of putrefaction and contagious diseases. These are microscopic plants which attach themselves to the dust particles and are borne around by them. They are called by the general name of bacteria. They are very diverse in appearance, and also in the effects produced by their lodgment and growth. They may be divided into two great classes: those which flourish only upon dead matter, animal or vegetable, and those which thrive only upon living animals or plants, and exist at their expense.

The former class are called saprophytes-that is, destroyers of dead things. They break up putrescible matter and reduce it to carbonic acid, ammonia, and other simple compounds, suitable for the immediate use of ordinary growing plants.

The other class of bacteria are true parasites. These are the dangerous ones. When one of them alights upon a living creature, upon a part which is both moist and warm, it begins at once to increase and multiply, some kinds slowly, and others with great rapidity. They not only rob the system by absorbing some of the fluids which should nourish the body, but they also produce virulent poisons which derange the system in various ways.

253. Ground Air

Ground Air. Ordinary soil, which is capable of supporting grass or producing a crop of vegetables, is in reality an extensive manufactory of gas. It is here that the myriads of saprophytes, already described, perform their work of decomposing all animal and vegetable remains into elementary substances suitable for the nutriment of living plants. The result of their operation is to produce large quantities of carbonic acid, together with various ammonia compounds, and, occasionally, sulphureted hydrogen. Free ammonia, however, occurs only in very small proportions.

Carbonic acid is also produced by the chemical interactions taking place between the mineral substances contained in the soil, the amount varying with the nature of the materials and the degree of moisture.

The production of gas is most copious in soil of moderate moisture; very dry earth produces but little. When the soil is constantly saturated with water, the processes are different, and the quantity of gas evolved is usually smaller.

254. Any excavation in the earth, such as a cellar, trench, or well, acts as a vent for the gases contained in the adjacent soil.

Ordinary cellars act as collecting basins for these earth gases; and, unless adequate ventilation is provided, they will pass up through the floor and diffuse into the rooms above. The inflow of gas cannot be stopped by facing the walls or bottom with Portland cement, because gases will pass through ordinary brick, mortar, and cement, about as readily as water will percolate through a stratum of fine sand. The cement will serve to retard the flow somewhat; but, in order to stop it, substances like asphaltum or paraffin must be used.