CRYPTOGAMS 309 
in a warm place till the usual indications of the presence 
of bacteria appear (347). The spores of this micro- 
organism are so resistant that they can withstand the tem- 
perature of boiling water for several hours, while those of 
most other forms of bacteria are killed by a few minutes’ 
exposure to it; hence, the crop that develops after boiling 
will consist of a pure culture of the 
hay bacillus. 
In their active state these organ- 
isms will be seen to consist of single- 
celled, rod-shaped bodies, about 
ae three or four times as long as broad, 
and generally cohering in 
bands or filaments, as shown 
in Fig.444,c. The black dots 
within the cells are the 
spores. Each individual 
bacterium produces but a 
single spore, or rather be- 
comes a spore itself, by the 
' contraction of its contents 
and the formation around 
them of a strong inclosing 
membrane. On germinat- 
Fics. 443, 444.— Hay bacillus (B. sub- 
tilis) : 443, aportion of the film fromthecul- | : : 
ture liquid, the black lines, e, being bacteria 1ng, the spores give rise to 
tion, oat motile celsead chainof ells: 6, little ciliated, one-celled or- 
non-motile cells; c, spores and chain of ganisms called “ owarm 
spores from the film e. ” . 
spores,” that swim about 
freely in the containing medium and multiply rapidly for a 
time by cell division. After this they pass again into the 
quiescent state, ready, whenever favorable conditions arise, 
to begin anew the repetition of their life cycle, which is an 
irregular alternation of cell division and spore formation. 
350. Resistance of spores. — Bacteriologists are not fully 
agreed as to the cause of spore formation, some holding 
that it takes place only when conditions are most favorable 
