dividing, appears as a short rod, and a short rod form after
dividing may be so short as to appear like a spherical organism.

With all these reasons for confusion, it is not to be wondered at
that no satisfactory classification of bacteria has been reached,
or that different bacteriologists do not agree as to what
constitutes a species, or whether two forms are identical or not.
But with all the confusion there is slowly being obtained
something like system. In spite of the fact that species may vary
and show different properties under different conditions, the
fundamental constancy of species is everywhere recognised to-day
as a fact. The members of the same species may show different
properties under different conditions, but it is believed that
under identical conditions the properties will be constant. It is
no more possible to convert one species into another than it is
among the higher orders of plants. It is believed that bacteria do
form a group of plants by themselves, and are not to be regarded
as stages in the history of higher plants. It is believed that,
together with a considerable amount of variability and an
occasional somewhat long life history with successive stages,
there is also an essential constancy. A systematic classification
has been made which is becoming more or less satisfactory. We are
constantly learning more and more of the characters, so that they
can be recognised in different places by different observers. It
is the conviction of all who work with bacteria that, in spite of
the difficulties, it is only a matter of time when we shall have a
classification and description of bacteria so complete as to
characterize the different species accurately.

Even with our present incomplete knowledge of what characterizes a