PBOTOPHTTA. 



109 



frequently appear in tightly closed vessels -whose contents 

 have been boiled. Some people have been led to explain 

 their appearance under such circumstances by " spontane- 

 ous generation;" but thus far the facts are capable of other 

 explanation. 



225. On account of their minuteness, bacteria may be 



fj v<o 



Fio. 46.— Forms of Bacteria, o, Micrococcus prodigiosus; 6, Bacterium termo 

 (resting stage); c. Bacterium lineola; d. Bacillus ulna; e. Spirillum rugula; /, 

 Spirocnsete plicatilis; g. Spirillum volutans. Magniiled 650 times. 



picked up by currents of air and borne long distances, and 

 in this way they are doubtless often carried from place to 

 place. When a pool of putrid -water dries up, the bacteria 

 with which it swarmed are blown away with the dust and 

 dirt, dropping everywhere into pools, upon plants and ani- 

 mals living and dead, and even entering our lungs with 

 the air we breathe. 



