MOVEMENT OF MICRO-ORGANISMS 11 



millions, 1 grain ; 289 billions, 1 pound. After twenty-four 

 hours the descendants from a single bacillus would weigh 

 •ftVf of a grain ; after two days, over a pound ; after three 

 days, sixteen and a half million pounds, or 7,366 tons. It 

 is quite unnecessary to state that these figures are purely 

 theoretical, and could only he realized if there were no impedi- 

 ment to such rapid increase. 



Fortunately for us, however, various checks, such as lack 

 of food and unfavourable physical conditions, prevent un- 

 manageable multiplication of this description. 



These figures show, however, what a tremendous vital 

 activity micro-organisms do possess, and it will be seen 

 later at what great speed they increase in water, milk, 

 broth, and other suitable nutrient media. 



Movement of Micro-organisms. — Many of the bacteria are 

 motile, especially the rod -like and spiral forms. This 

 movement, in some of the bacteria, at least, is induced by 

 one or more little hair-like or whip-like processes attached 

 to the ends or body of the organism. These little projec- 

 tions, or cilia, are known as 'flagella.' By means of these 

 minute threads of protoplasm, whiqh perform lashing 

 movements, the bacteria go through a most elaborate and 

 astonishing series of movements, sometimes very rapid, at 

 other times very slow and sinuous. They roll over, dart 

 about, bang agaiast one another, rest awhile, and so on 

 through various phases of movement. Other micro- 

 organisms, particularly in the case of the cocci, are quite 

 motionless. This motility of the bacteria must not be con- 

 founded with oscillatory movements, or with such motions 

 as occur when solid particles are suspended in a fluid 

 medium, which is due to electrical disturbance, and generally 

 called the ' Brownian movement.' 



The following bacilli, amongst others, have numerous 

 flagella distributed over the whole of the organism : The 



