140 



NATURE OF BACTERIA 



together in colonies is due to the mucilaginous excretion from 

 their bodies which is often brightly colored. Bacteria range 

 from globular to rod-like and curved forms (Fig. 91). Many 



Fig. 91. Forms of bacteria : A, Bacillus subtilis, a form common in hay 

 infusions. 1, motile state; 2, cells with spores; 3, slimy mass of bacteria, 

 the zooglea condition, that appears on the surface of infusions, cooked 

 vegetables, etc. B, Spirillum. C, a coccus form that appears in pus. D, 

 mobile and spore stage of lock-jaw bacillus. 



are motile by means of cilia, as in the case of the zoospores of 

 the Myxomycetes, which project singly or in tufts from the ends 

 of the cells or in varying numbers from all sides. 



(a) Reproduction of Bacteria. — This is a simpler process than 

 in the slime moulds and much more rapidly effected when the 

 conditions are favorable for growth. This process consists of 

 forming a partition through the middle of a cell when the two 

 daughter cells thus formed separate at once or they may remain 

 attached, forming ultimately a chain of cells, since these two new 

 cells continue to grow and repeat the dividing process. This 

 method of multiplication goes on with great rapidity, frequently 

 within a half hour, so that many millions of plants may be formed 

 in a day from a single bacterium. This accounts for the rapidity 

 with which solutions, as beef tea, in which bacteria thrive, be- 

 come turbid and also for the gelatinous masses and wrinkled 



