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BACTERIA.                              33


As a rule, the spherical organisms are the smallest and
the spiral organisms the longest, except the chains of
bacilli called leptothrix. Their measurements vary from
o. 15 jj. (micrococcus of progressive abscess-formation in
rabbits) to 2.8 p (Diplococcus albicans am plus) for cocci,
and from i X 0.2 p. (bacillus of mouse-septicemia) to
5 X 1.5 p. (anthrax bacillus) for bacilli. Some of the
spirilla are very long, that of relapsing fever measuring
40 p at times.

This estimation of size almost prepares one for the
estimation of weight given by Nageli, who found that
an average bacterium under ordinary conditions weighed

looooooinmr °f a milligram.

The bacteria multiply in two ways : by direct division
(fission) and by the development of spores, seeds, or eggs
(sporulation). The more common mode is by binary
division. The bacterium which is about to divide ap-
pears a little larger than normal, and, if a spherical
organism, more or less ovoid. No karyokinetic changes
have been observed in the nuclei, though they may occur.
When the conditions of nutrition are good, the process of
fission progresses with astonishing rapidity. Buchner
and others have determined the length of a generation
to be from fifteen to forty minutes.

The results of binary division, if rapidly repeated, are
almost appalling. u Cohn calculated that a single germ
could produce by simple fission two of its kind in an
hour ; in the second hour these would be multiplied to
four ; and in three days they would, if their surroundings
were ideally favorable, form a mass which can scarcely be
reckoned in numbers, or, if reckoned, could scarcely be
imagined—four thousand seven hundred and seventy-two
billions. If we reduce this number to weight, we find
that the mass arising from this single germ would in
three days weigh no less than seventy-five hundred
tons." u Fortunately for us," says Woodhead, "they
can seldom get food enough to carry on this appalling
rate of development, and a great number die both for