242 ESSENTIALS OF BOTANY 
the contents with air containing living bacteria, no putre- 
faction can occur. Canned goods may be kept unspoiled 
for an indefinite number of years, not because all the 
Fic. 169. Bacteria stained to show Cilia. 
A, Bacillus subtilis, found in hay infusions; B, Spirillum undula, found 
in water containing decaying fish, alge, etc.; C, species of Pseudomo- 
nas; D, Planococcus citreus, which forms yellow patches on various 
substances; E, Bacillus typhi, the cause of typhoid fever; F, Micro- 
spira comma, the cause of Asiatic cholera. 
air has been driven out of the cans, but because they and 
everything in them has been sterilized by heat. Bacteria 
in the active growing condition cannot live if exposed 
