bacteriologists to discern different species (Fig. II). All these
points of difference are of practical use to the bacteriologist in
distinguishing species.

SPORE FORMATION.

In addition to their power of reproduction by simple division,
many species of bacteria have a second method by means of spores.
Spores are special rounded or oval bits of bacteria protoplasm
capable of resisting adverse conditions which would destroy the
ordinary bacteria. They arise among bacteria in two different
methods.

Endogenous spores.--These spores arise inside of the rods or the
spiral forms (Fig. 12). They first appear as slight granular
masses, or as dark points which become gradually distinct from the
rest of the rod. Eventually there is thus formed inside the rod a
clear, highly refractive, spherical or oval spore, which may even
be of a greater diameter than the rod producing it, thus causing
it to swell out and become spindle formed [Fig. 12 c]. These
spores may form in the middle or at the ends of the rods (Fig.
12). They may use up all the protoplasm of the rod in their
formation, or they may use only a small part of it, the rod which
forms them continuing its activities in spite of the formation of
the spores within it. They are always clear and highly refractive
from containing little water, and they do not so readily absorb
staining material as the ordinary rods. They appear to be covered
with a layer of some substance which resists the stain, and which
also enables them to resist various external agencies. This
protective covering, together with their small amount of water,