38 PA THOGENIC BA CTERIA.
in chains or solitary and are surrounded by an encase-
ment almost cartilaginous in consistence, has been called
Certain bacteria, constituting a better-known if not
more important group, are not spherical, but elongate*
or u rod-shaped," and bear the name bacillus (Fig. 3).
_^J^§^£_ —- —•
FIG. 3.—Diagram illustrating the morphology of the bacilli: a, b, c, various
forms of bacilli; d, e, bacilli with flagella; f, chain of bacilli, individuals dis-
tinct; £, chain of bacilli, individuals not separated.
I would remark that the absence of a standard by
which to separate the cocci from the bacilli is the cause
of much confusion. In the judgment of the author, it
would be well to place all individuals having one diam-
eter greater than the other among the bacilli. This
would prevent the error of describing one species as
uoval cocci" and another as "nearly round bacilli,"
and by giving a definite standard would greatly aid in
the formation of a differential table.
The bacilli present a considerable variety of forms.
Some are quite short, with rounded ends, so as to ap-
pear elliptical; some are long and delicate. Some have
rounded ends, as subtilis ; others have square ends, as
anthrax. Some are enormously large, some exceedingly
small. Some are always isolated, never forming threads
or chains ; others nearly always occur in these forms.
The bacilli always divide by transverse fission, so that
the only peculiarity of arrangement is the formation of
threads or chains.
In the older writings the short, stout bacilli were all
described under the generic term bacterium. This genus,
like some of the species it comprehended, has now passed