DIPHTHERIA. 285

among the well-formed individuals which abound in
fresh cultures a large number of peculiar organisms are
to be found, some much larger than normal, some with
one end enlarged to a club-shape, some greatly elongated,
with both ends expanded into club-shaped enlargements.
These bizarre forms seem to represent an involution-form
of the organism, for, while present in perfectly fresh cul-
tures, they are so abundant in old cultures that scarcely
a single well-formed bacillus can be found. It not infre-
quently happens that in unstained bacilli distinct gran-
ules can be defined at the ends—polar granules—thus
giving the organism somewhat the appearance <of a
diplococcus.

The bacillus can be readily stained by aqueous solu-
tions of the anilin colors, but more beautifully and
characteristically with Loffler's alkaline methyl ene blue:

Saturated alcoholic solution of methylene blue, 30 ;
i: 10,000 aqueous solution of caustic potash, 100 ;

and an aqueous solution of dahlia, as recommended by
Roux.

When cover-glass preparations are stained with these
solutions, the bizarre forms already mentioned are much
more obvious than in the unstained individuals, and
the contrast between the polar granules, which color in-
tensely, and the remainder of the bacillus, which tinges
slightly, is marked. Through good lenses the organisms
are always distinct bacilli, notwithstanding the fact that
the ends stain more deeply than the centres, and it is
only through poor lenses that the organisms can be mis-
taken for diplococci. The bacilli stain well by Gram's
method, this being a good method to employ for their
definition in sections of tissue, though Welch and Abbott
assert that Weigert's fibrin method and picro-carmin give
the most beautiful results.

The diphtheria bacillus does not form spores, and is
delicate in its thermal range. Loffler found that it could
not endure a temperature of 60° C., and Abbott has shown