FORM AND STRUCTURE OF BACTERIA 35 



Rapidity of Movement. Viewed under the microscope the 

 motile bacteria seem to move very swiftly. This idea is, of 

 course, due to the limited field of vision. Fischer estimates 

 the actual average rate of movement under normal conditions 

 of temperature, etc., at ten centimeters in fifteen minutes, or 

 about ^ millimeter per second. It should be noted that the 

 speed is comparatively rapid, taking into consideration the 

 small size of the bacterial cell. The rapidity of movement of a 

 motile bacterium varies with the physiological condition of 

 the cell. The temperature, presence of nutrient material, 

 presence of excretory products, and the general vitality of the 

 cell have much to do with the character of the movement of 

 the cell. 



Brownian Movement. Very frequently when preparations 

 of live bacteria are examined under the microscope they are 

 seen to move backward and forward in an oscillating fashion. 

 They do not progress through the medium. This movement 

 should be carefully differentiated from true locomotion. This 

 phenomenon, which was first described by Brown, is due to 

 the bombardment of molecules in the liquid medium in which 

 the bacteria may be suspended. Particles of India ink show 

 the same sort of movement. 



Capsules. Some species of bacteria secrete a gelatinous 

 substance from the outer layers of the cell protoplasm or the 

 cell wall. When large numbers of bacteria are found together 

 secreting these gelatinous substances in great amount the 

 typical zooglcea is formed. However, the bacteria may oc- 



