AGf~ICULTURAL RESEARCH, PUSA.

8 PRAC'l'ICAL BACTERIOLOGY
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microscope field (vide p. 57). Brownian movement
is generally regarded as due to the impact of the
molecules of the medium in which the organisms are
suspended and is an oscillatory movement within a
limited radius.
Flagella may be "terminal "-i.c. at one or both
ends of the bacterium-and single or mllltiple. They
may be distributed all round the organism, and this
arrangement is described as " peritrichate. "
When there is a single terminal flagellum the term " monotrichate
" is applied; .. amphitricl1ate " indicates thc presence
of a flagellum at each pole; " lophotrichate" refers to the
arrangement of multiple f1agclla at one or both poles.
Among the spirochaet.es motility is generally due
to contractions of the cell body. Though certain
spirochaetes have been described as possessing flagellalike
structures, these organisms are regarded as
characteristically devoid of flagella.
BACTERIAL SroREs.-Smne species develop a highly
resistant resting-phase, 01' spore, by which the individual
survives unfavourable external conditions. The
spore is not a reproductive structure. In the vast
majority of spore-bearing species only one spore
is developed by each vegetative i'm'm. This structure
appears in the cell protoplasm (" endogenous ") and
increases in size, appearing as a round, ovaloI'
elongated body, which may be situated in the centre
of the bacterium (" central "), at the end (" terminal "),
or between the centre and end (" subterminal "). The
relative size of the spore varies with different species.
Spores can withstand all injurious chemical and
physical influences better than the vegetative forms,
and owe certain of their resistant properties to a
dense outer protective membrane. Under favourable
external conditions the membrane ruptures and the
vegetative form is resumed. This process is described
as the " germination " of thc spore.
'l'he spore is not stained by the ordinary methods but
appears as a clear, unstained portion of the bacterial