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MICROBES OF THE AIR

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Robert L. Gute .

July 30th,

1896.
MICROBES IN TH AIR,

It has been observed for a considerable time that the
air is filled with small floating bodies. In shade or sun-
shine, these floating bodies are not observed as readily as
when a beam of light passes into a somehat darkened room.
On a windy day we have all observed the dust in the air. It
is composed of fine particles of sand, remnants of animal
substance, or decayed vegetable product. The dust then, may
include mineral, animal or vegetable matter. Laying aside
the two former divisions let me direct your thought to the
vegetable world and investifate the floating bodies found
therein.

These micro-organisms or bacteria as: the scientist calls
them, were discovered in the early part of the seventeenth
century. At this time it was supposed that nothing was

living that could not be seen. But by the earnest work of
Cohn, Koch, Roberts and Pasteur a new science known as
Bacteriology has been added to the field of research.

These men studied the minute organisms, observed their mode
of growth, shape, color and manner of life in general. But
not ‘till the middle of this century has this science been
brought into prominence. The study of pathology has been
placed on a scientific basis, showing that most of our dis-
eases are caused by a specific micro-organisnm. Other germs

are known which are non-pathogenic or do not produce disease

94901
The are also divided into liquefying and non-liquefying accord-
ing to their ability to liquify gelatin. Parasites are

thus living on the body of living matter and Saprophysites
live on dead matter. There are many other calssifications
but this will be sufficient for a general description.

In studying microbes found in the air, two methods are
used, namely the Petri dish and the Hess apparatus. As the
former is the shorter method, it will be considered first,
outlining work done and the results obtained.

PETRIE DISH - The bottom of three sterilized petrie
dishes were covered with agar, which hardened when cooled.

To sterilize the petrie dishes they were previously heated in
an oven at 150 degrees C. for over one hour. Care was
taken in pouring in the above agar as not to lift the lid
higher than was necessary, as the microbes in the air grav-
itate and might innoculate the medium. This agar is a pre-
paration of meat extract, peptone, common salt, and water
and when sterilized and placed in sterilized tubes is ready
for use. These tubes are stoprered with cotton as this
prevents the germs in the air from entering.

These three petrie dishes were exposed for about two
minutes in three different places namely; dairy, horse stable
and silo. The following day a slight growth was observed in

the dish exposed in the stable. At the second day colonies
had developed in all A microscopical examin:tion was not
made, but if the size, shape and color of t’:e colonies and
mould are characteristic of diff rent germs, the dish from
the dairy room indicated six kinds of colonies and three
kinds of mould; from the stable six colonies and three mould,
and from the silo three colonies and two mould. Some of the
colonies were colored bright red, others buff and some white.
The mould colonies were colored either green, black or white.
From this experiment it is shown that there are several kinds
of germs and moulds in the air.

But with the Hess apparatus more definite results were
obtained. Besides showing that the air contained several
different kinds of microbes, it also indicated the number of
germs in a given quantity of air.

HESS APPARATUS - It consists of a glass tube two feet
long and sever inches in circumference. One end is covered
over by a thin sheet of rubber stretched rather thght and
tied on with a string. This rubber has a small aperture
for the admission of air. This end is again covered by a
large and thick rubber. The other end of the tube is closed
by a rubber cork and passing through the center of this is
a glass tube filled with cotton. This part of the apparat-
us after being thoroughly cleaned and dried, was placed in

a steam sterilizer and kept there for one hour, the tempera-
ture being nearly one hundred centeprade. Then took the tube
out, held it nearly horizontal, removed the rubber stopper
and poured into the tube sufficient agar to coat the entire
inner surface, rotating the tube at the same time. Return
the cork and cool the agar by revolving the tube in ice-water.
When this is completed return the tube on the tripod and pro-
ceed with the aspirator. By the aid of two one liter flasks
one of them being filled with water, rubber tubing connectin;
it with the sterilized tube. The second flask 3. is below
A. and receives the water when siphoned through. When all
is ready the outer rubber covering is removed and the siphon
started. By adjusting the height of flask B. the rapidity
of tne air that enters the tube can be regulated. The air
examined was from the labatory over the entrance, the date
being July 12th, 1896. Five liters of air were drawn tnrough
the tube at the rate of one liter in two minutes. The follow-
ing day several colonies could be seen, after the second day
they were thick. A micrometer, composed of a sheet of paper
with a square inch removed from the center, was placed over
several different places on tne tube and t e colonies counted
As the result it was estim:ted that (10351) colonies were
present. This would place about 2070 in each liter of air.
Some of the colonies were minute grey specks and could hardly
be seen with the naked eye, others were somewhat larger but

of the same shape. Some resembled a celery leaf in form am
one in particular was similar to a large branching bush, at
least two inches across.

A microscopical examinetion showed that th-re were at
least four different kinds of germs, three bacilli and one
Micrococcus.

By repeatedly examining the air in different localities,
an average of the number of microbes could be obtained, and
by examining the petrie dishes in the hospitals, alleys of
large cities and other places, a thorough examin tion of
the germs there found, and continued work of classifying them

would be of rfreat interest.
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