CHAPTER II 



THE BEHAVIOR OF BACTERIA 



I. Structure and Movements 



Bacteria are perhaps the lowest organisms having a definite form 

 and special organs for locomotion. In these characteristics they are less 

 simple than Amoeba and resemble higher animals, though in other ways 

 the bacteria are among the simplest of organisms. Whether they are 

 more nearly related to animals or to plants is a question of little impor- 

 tance for our purposes ; they are usually considered as nearer to plants. 

 Bacteria are minute organisms living in immense numbers in decay- 

 ing organic matter, and found in smaller numbers almost ever)rwhere. 



They have characteristic definite 

 forms (Fig. 23); some are straight 

 cylindrical rods; some are curved 

 rods; some are spiral in form; 

 others are spherical, oval, or of 

 other shapes. The individuals are 

 often united together in chains. 



While some bacteria are quiet, 

 others move about rapidly. The 

 movements are produced by the 

 swinging of whipHke protoplasmic 

 processes, the flagella or cilia. The 

 flagella may be borne singly or in 

 numbers at one end of the body, 

 or may be scattered over the entire 

 surface. Figure 23 shows the dis- 

 tribution of flagella in a number 

 of species. 

 In most bacteria we can distinguish a permanent longitudinal axis, 

 and along this axis movement takes place. Thus both the form, and in 

 correspondence with it, the movement, are more definite than in Amoeba. 

 If the bacterium is quiet, we can predict that when it moves it will move 

 in the direction of this axis; for Amoeba such a prediction cannot be 



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Fig. 23. — Difterent species of bacteria, 

 showing the distribution of the flagella. a, 

 Chromatium okeni, after Zopf ; b, Chro- 

 matmm photometricum, after Engelmann ; 

 c. Spirillum undula, after Migula; d. Vibrio 

 cholera, after Fischer ; e. Bacilli of typhus, 

 after Fischer ; /, Bacillus syncyaneus, after 

 Fischer ; g, Clostridium butyricum, after 

 Fischer. 



