In a similar way we have the
pus-causing grape coccus of a golden color (staphylococcus pyogenes
aureus). It grows with the individual plants arranged somewhat after
the manner of a bunch of grapes, and when millions of them are
collected together, the mass has a golden yellow hue. Again, we have
the bacillus tuberculosis, the rod-shaped plant which is known to
cause tuberculosis of the lungs, joints, brain, etc.
It is hardly astonishing that these fruitful sources of disease have
so long remained undetected, when their microscopic size is borne in
mind. That some of them do cause disease is indisputable, since
bacteriologists have, by their watchful and careful methods, separated
almost a single plant from its surroundings and congeners, planted it
free from all contamination, and observed it produce an infinitesimal
brood of its own kind. Animals and patients inoculated with the plants
thus cultivated have rapidly become subjects of the special disease
which the particular plant was supposed to produce.
The difficulty of such investigation becomes apparent when it is
remembered that under the microscope many of these forms of vegetable
life are identical in appearance, and it is only by observing their
growth when in a proper soil that they can be distinguished from each
other.
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