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class is not of much interest to us in pathology, yet there are
a few varieties of lesser note that produce pathological re-
sults that are regarded as anaerobic micro-organisms. The
great bulk belong to the indifferent aerobic.
Now, among those that are indifferently aerobic there
are degrees of indifference that are important. For instance,
the yeast plant, when it grows upon the surface of a liquid
and is exposed to the air, will grow very much more abun-
dantly, make more yeast, but it will not make so much alco-
hol when it grows at the bottom of the liquid and the car-
;
bonic acid that is given off has excluded all free oxygen, it
will not grow very rapidly, it will not make yeast very abun-
dantly, but it will make a great deal more alcohol. So that
the condition of growth with air and without air makes a
great difference in the action of the plant in the decomposi-
tion of the material on which it feeds.
Then, again, the Staphylococcus Aureus, one of the
pus-forming micro-organisms that we see very frequently,
when growing upon the surface of the culture medium, is a
golden yellow, almost exactly the color of the bright yellow
color of the flowers of the golden rod, but when growing in
the depths of the medium, where air is excluded, it has no
color whatever. So that there are degrees of this indifference
to oxygen, and these differences of the exclusion and admis-
sion of oxygen produce various differences in the results of
microbic growths.
There are a large number of anaerobic micro-organisms
that seem confined to the putrefactive processes. Foi these
to do their work it is necessary that putrefaction be begun
by other organisms that are indifferent to the air, beginning
on the outside. The spores of the anaerobic organisms are
carried into the flesh as it begins to decompose, and as the
air is excluded from them they begin to grow, and they
produce those extremely foul odors that we will find pro-
duced in the interior of decaying flesh, and melt down the
whole very rapidly. These various characteristics appear in
different species of micro-organisms, and through differences
in the conditions under which they grow.
Then again, and the last division I will give you this
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