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BACTERIA.                              37

multiply by fission the resulting two organisms not
infrequently remain attached to each other, producing
what is called a diplococcus (Fig. 2, b). The diplococci
sometimes consist of two perfect spheres, but more often
^show a flattening of the contiguous surfaces, which are
not in absolute apposition (Fig. 2, g). In a few cases, as
the gonococcus, the approximated surfaces are slightly
concave, causing the organism to somewhat resemble the
German biscuit called a ccsemmel,n hence biscuit- or
semmel-cocci (Fig. 2, //). Frequently a second binary di-
vision occurs, causing four individuals to remain closely
approximated, without disturbing the arrangement of the
first two. When division of this kind produces a distinct
tetrad, the organism is described as a tetragenococcus,
while to the entire class of cocci dividing so as to pro-
duce fours, eights, twelves, etc. on the same plane the
name merismopedia is given (Fig. 2, e and f).

If, as sometimes happens, the divisions take place in
three directions, so as to produce cubical masses or "pack-
ages" of cocci, the resulting aggregation is described as
a sarcina (Fig. 2, 2). This form slightly resembles a dice
or a bale of cotton in miniature.

If the divisions always take place in the same direc-
tion, so as to produce a chain or string of beads, the
organism is described as streptococcits (Fig. 2, d\ When
there are diplococci joined in this manner a strepto-diplo-
coccus is of course formed.

More common than any of the forms already described
is one in which, without any definite arrangement, the
cocci occur in irregular groups having a fancied resem-
blance to bunches of grapes. These are called staphylo-
c&ci, and, as it is very unusual to find cocci habitually
occurring isolated, most cocci not classified under one of
the above heads are called staphylococci.

When cocci are associated in globular or lobulated
clusters encased in a resisting glutinous, homogeneous
mass, the name ascococcus has been used in describing
them. A modified form of this, in which the cocci are