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 withstantl 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 

 ..- '.„','- 'V' hay bacillus. 

 .- ;'V/ ''"',,■ - ' - ' In their active state these organ- 

 '■' - --' ,,. ' ^. ' isms will be seen to consist of single- 



''"•':^A-'^^^^ celled, rod-shaped bodies, about 

 three or four times as long as broad, 

 and generally cohering in 



443 



ci'mr^^ 



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- 

 ing, the spores give rise to 

 little ciliated, one-celled or- 

 ganisms called ■' swarm 

 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 



444 



Figs. 443, 444. — Hay bacillus (/?. sub- 

 tilis) : 443, a portion of the film from the cul- 

 ture liquid, the black lines, c, being bacteria 

 in the vegetative state ; 444, spore forma- 

 tion ; a, d, motile cells and chain of cells : h, 

 non-motile cells ; c, spores and chain of 

 spores from the film e. 



