Now, to apply this: before a thunder-storm, everything has been so still for days that the oxygen in the air has been to some extent robbed of its life-sustaining power. The air feels “close,” a feeling of drowsiness comes over all. But, after the air has been pierced by several flashes of lightning, the life-force in the air is restored. Your spirits revive; you feel restored; your breathing is far freer; your drowsiness is gone. Then there is a burst of heavenly music from the exhilarated birds. Thus a thunder-storm “clears the air.”
After the passage of lightning through the air ozone is produced—the gas that is produced after a flash of electricity. It is a kind of oxygen, with fine exciting effects on the body. If, then, the life-sustaining power of oxygen depends on a trace of ozone, and this is being made by lightning’s work, how pleased should we be at the occasional thunder-storm!
CHAPTER XV
DISEASE-GERMS IN THE AIR
The gay motes that dance in the sunbeams are not all harmless. All are annoying to the tidy housekeeper; but some are dangerous. There are living particles that float in the air as the messengers of disease and death. Some, falling on fresh wounds, find there a suitable feeding-place; and, if not destroyed, generate the deadly influence. Others are drawn in with the breath; and, unless the lungs can withstand them, they seize hold and spread some sickness or disease. From stagnant pools, common sewers, and filthy rooms, disease-germs are constantly contaminating the air. Yet these can be counted.
The simplest method is that of Professor Frankland. It depends on this principle: a certain quantity of air is drawn through some cotton-wool; this wool seizes the organisms as the air passes through; these organisms are afterwards allowed to feed upon a suitable nutritive medium until they reach maturity; they are then counted easily.
About an inch from each end of a glass tube (5 inches long and 1 inch bore), the glass is pressed in during the process of blowing. Some cotton-wool is squeezed in to form a plug at the farther constricted part of the glass. The important plug is now inserted at the same open end, but is not allowed to go beyond the constricted part at its end. A piece of long lead tubing is attached to the former end by an india-rubber tube. The other end of the lead tubing is connected with an exhausting syringe. Sixty strokes of the 18 cubic inches syringe will draw 1080 cubic inches of the air to be examined through the plugs, the first retaining the organisms.
The impregnated plug is then put into a flask containing in solution some gelatine-peptone. The flask is made to revolve horizontally until an almost perfectly even film of gelatine and the organisms from the broken-up plug cover its inner surface.
The flask is allowed to remain for an hour in a cool place, and is then placed under a bell-jar, at a temperature of 70° Fahr. There it remains, to allow the germs to incubate, for four or five days. The surface of the flask having been previously divided into equal parts by ink lines, the counting is now commenced. If the average be taken for each segment, the number of the whole is easily ascertained. A simple arithmetical calculation then determines the number of organisms in a cubic foot, since the number is known for the 1080 cubic inches. That is the process for determining the number of living organisms in a fixed quantity of air.