8o MORPHOLOGY AND CULTUIUE OF MICROORGANISMS 



tive positions. In other cases the movement is vibratory, the bacteria 

 move back and forth but do not progress or change their relative 

 positions to any extent. This latter form of inovement is known as 

 brownian movement, because it was first described by Brown. 



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 Uf e, 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 utider 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 tihty 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 defijiitely 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 wiU be no change. 



Organs of Locomotion. — The protoplasmic threads referred to as 

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

 between the cilium and flagellum is the fact that a ciUum 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 



