repeats the process. This method of multiplication by simple
division is the distinguishing mark which separates the bacteria
from the yeasts, the latter plants multiplying by a process known
as budding. Fig. 2 shows these two methods of multiplication.

While all bacteria thus multiply by division, certain differences
in the details produce rather striking differences in the results.
Considering first the spherical forms, we find that some species
divide, as described, into two, which separate at once, and each
of which in turn divides in the opposite direction, called
Micrococcus, (Fig. 3). Other species divide only in one direction.
Frequently they do not separate after dividing, but remain
attached. Each, however, again elongates and divides again, but
all still remain attached. There are thus formed long chains of
spheres like strings of beads, called Streptococci (Fig. 4). Other
species divide first in one direction, then at right angles to the
first division, and a third division follows at right angles to
the plane of the first two, thus producing solid groups of fours,
eights, or sixteens (Fig 5), called Sarcina. Each different
species of bacteria is uniform in its method of division, and
these differences are therefore indications of differences in
species, or, according to our present method of classification,
the different methods of division represent different genera. All
bacteria producing Streptococcus chains form a single genus
Streptococcus, and all which divide in three division planes form
another genus, Sarcina, etc.

The rod-shaped bacteria also differ somewhat, but to a less
extent. They almost always divide in a plane at right angles to
their longest dimension. But here again we find some species