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 deg. 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.
No less than thirty colonies of organisms were counted in a cubic foot of
air taken from the Golden Gallery of St. Paul's Cathedral, London, and 140
from the air of the churchyard. An ordinary man would breathe there
thirty-six micro-organisms every minute.
Electricity has a powerful effect in destroying these organisms. Ozone is
generated in the air by lightning, and it is detrimental to them. In fine
ozoned Highland air scarcely a disease-germ can be detected. Open sea air
contains about one germ in two cubic feet. It has been found that in Paris
the average in summer is about 140 per cubic foot of air, but in bedrooms
the number is double. During the twenty-four hours of the day the number
of germs is highest about 6 A.M., and lowest about mid-day.
Raindrops carry the germs to the ground. Hence the advantage of a thunder
plout in a sanitary way. A cubic foot of rain has been found to contain
5500 organic dust-germs, besides 7,000,000,000 of inorganic
dust-particles. In a dirty town the rain will bring down in a year, upon a
square foot of surface, no less than 3,000,000 of bacteria, many of them
being disease-bearing and death-bearing. No wonder, then, that scientific
men are using every endeavour to protect the human frame, as well as the
frame of the lower animals, from the baneful inroads of these floating
nuclei of disease and death.