BACTERIA 83 



very slowly. Many of them appear to move with wonderful rapidity. 

 Van Leeuwenhoek, when he first saw these moving bacteria, said that 

 they traveled with such great rapidity that they tore through one 

 another, but it must be borne in mind that under the high powers of 

 the microscope the rate of movement is magnified to the same extent 

 as the object, and that in reality the rate of movement is not excessive. 

 When compared to their size, the rate of movement is probably little 

 greater than that of a trotting horse and considerably less than that 

 of a speeding automobile or a railroad train. 



REPRODUCTION* 



Reproduction among the bacteria is largely asexual and takes place 

 ordinarily by what is known as binary fission. In addition to this a 



QOQDODOQ 



FIG. 62. The division of bacterial cells (diagrammatic). (After Novy.} 



number of bacteria go into a resting stage, or produce spores. The 

 spore formation is not, however, a method of multiplication, because 

 usually only a single spore is formed in a cell, but serves to tide the 

 organism through unfavorable conditions. 



VEGETATIVE MULTIPLICATION. This is accomplished by means of 

 binary fission (Fig. 62). When a bacterium has reached maturity, fis- 

 sion begins. Division begins by an invagination of the protoplasm 

 in the middle of the cell, which proceeds until the cell protoplasm is 

 completely separated. The cell wall then grows in and finally splits 

 forming the two ends of the new cells. These new cell walls are formed 

 at right angles with the long axis of the cell in the case of the bacilli 

 and spirilla, except in rare instances. In the case of micrococci, the 

 throwing of the cell wall across one diameter is quite as economical 

 as any other and may therefore proceed in any direction. Migula 

 makes a considerable point of the fact that bacilli and spirilla elon- 

 gate before division and micrococci divide before they elongate; this 



Preparedly W. D. Frost. 



