PB0T0PH7TA. 129 



in any exposed substance which is capable of furnishing 

 them with food. Some of the species live in the watery 

 juices of plants and animals, causing various diseases. 



226. Some bacteria can endure high temperatures, and 

 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. 



227. The proper spores of bacteria {endospores) are pro- 

 duced singly within the cells. By the breaking of the fila- 

 ments into their component cells other reproductive bodies 

 {arthrospores) are formed. 



228. On account of their minuteness, bacteria may be 

 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. 



The Bacteria (Bacteriaceie) are here treated as one of the families 

 of the Nematogeneee, but they should rather be treated as degenerated 

 species and genera of Oscillariacese and Nostocacese. Among those 

 of especial interest to us are the following : 



1. The bacterium of small-pox (Streptococcus variolse), composed of 

 minute globular cells, is now accepted as the cause of small-pox. 

 That found in vaccine virus is a cultivated state, while that in small- 

 pox is its virulent state. 



3. The bacterium of ordinary putrefaction (Bacterium termo, Fig. 

 62, 6) is composed of oblong cells. It is the cause or accompaniment 

 of all ordinary decay of animal and vegetable substances. 



3. The bacterium of apple-blight (Bacillus amylovorus) is the cause 

 of a troublesome disease of apple-trees. 



4. The bacterium of anthrax (Bacillus anthracis) is composed of 



