4 Dairy Bacteriology. 



they are called endospores. The protoplasm of the endo- 

 spore contracts into a small ball, and finally acquires a 

 thickened outer part that enables it to resist unfavorable 

 surroundings; therefore, they are adapted to the perpetua- 

 tion of the species under severe conditions, and are analo- 

 gous in this respect to the seeds of higher plants. Many 

 of the bacilli form spores, the cocci do not. Spores do not 

 germinate and grow as readily as the ordinary cells. 



7. Movement. Many bacteria are unable to move 

 about from place to place. They have, however, a vibra- 

 tory movement known as the Brownian motion, that is 

 purely physical. Many other forms possess an ability to 

 move about. This they do by means of fine thread-like 

 processes on the edge of the cell known as cilia (sing. 

 cilium) . Coccus forms in general are non-motile, while 

 bacilli may or may not possess these locomotor organs. 



8. Classification. In arranging bacteria according 

 to their various relationships, difficulties are experienced 

 that do not obtain with the higher forms of plants. 

 There exists so little difference between the various spe- 

 cies as regards form and size that it becomes necessary 

 to employ other characters of a physiological nature, as 

 for instance the way in which the germ develops in cul- 

 ture media, the by-products that are formed as a result 

 of growth and other characters of a similar nature. 



