82 MORPHOLOGY AND CULTURE OF MICROORGANISMS 



BROWNIAN MOVEMENT.- -This movement is probably caused by the 

 impact of the molecules of the suspending medium and for this reason 

 is sometimes called molecular movement. It is not characteristic of 

 bacteria, or indeed of life, but is shared by many small microscopical 

 objects when suspended in a fluid medium. Most beautiful examples 

 of brownian movement can be seen by suspending granules of India 

 ink or carmine and examining them under the microscope. This 

 brownian movement is to be sharply differentiated from vital movement 

 which is possessed by some bacteria. 



VITAL MOVEMENT. As already indicated, bacteria have the power 

 of independent movement due to inherent vital power. ' Only a few of 

 the micrococci are motile, while many of the bacilli and spirilla are. This 

 movement is a change of position and is caused by certain protoplasmic 

 processes which these bacteria possess, known as cilia (sing, cilium) or 

 flagella (sing, flagellum}. The fact of motility or non-mo tility of an 

 organism is of considerable value to the systematist. It is determined 

 by examination in a hanging drop. At times, however, it varies so little 

 from the brownian movement that it is difficult to tell whether a par- 

 ticular organism or culture does or does not possess vital movement. 

 An opinion can be more definitely formed at times if some chemical 

 producing an anaesthetizing effect on the bacteria is introduced into 

 the examining medium. In case the organism is actually motile its 

 movement will be altered by the anaesthetic but in case it is merely a 

 brownian movement there will be no change. 



ORGANS OF LOCOMOTION. The protoplasmic threads referred to as 

 the organs of locomotion are known as flagella, or cilia. The difference 

 between the cilium and flagellum is the fact that a cilium has a simple 

 curve while a flagellum has a compound curve, like a whip lash. Most 

 of the bacteria possess flagella rather than cilia. The size, arrange- 

 ment, etc., of these flagella are constant and characteristic of a par- 

 ticular organism. Their structure and arrangement, therefore, will be 

 discussed later. 



CHARACTER OF MOVEMENT. Different bacteria exhibit different 

 kinds of movement. Some dart forward with great rapidity, others 

 move slowly; some move in straight lines, others wobble, but any 

 particular character is quite constant and many of the bacteria may 

 be recognized by their peculiar movements. 



RATE. The rate at which the bacteria travel when they possess 

 vital movement varies greatly. Some of them move very fast, others 



