se no disease, while
the other will produce perhaps tuberculosis of the lungs or brain.

Many scores of bacteria have been, by patient study, differentiated
from their fellows and given distinctive names. Their nomenclature
corresponds in classification and arrangement with the nomenclature
adopted in different departments of botany. Thus we have the
pus-causing chain coccus (streptococcus pyogenes), so-called because
it is globular in shape, because it grows with the individual plants
attached to each other, or arranged in a row like a chain of beads on
a string, and because it produces pus. 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. In certain cases it is quite difficult to distinguish them by
the physical appearances produced during their growth. Then it is only
after an animal has been inoculated with them that the individual
parasite can be accurately recognized and called by name. It is known
then by the results which it is capable of producing.

The various forms of bacteria are recognized, as I have said, by their
method of growth and by their shape. Another means of recognition is
their individual peculiarity of taking certain dyes, so that special
plants can be recognize