CHAPTER III. 

 THE LIFE HISTORY OF BACTERIA. 



Growth and multiplication is a characteristic of living- 

 organisms. As a rule the plant or animal cell, when it 

 reaches the fully developed, adult stag^e, divides and thus 

 g-ives rise to two new cells. The young- bacterial cell, like- 

 wise, grows, attains its full size, and then multiplies by 

 division or fission. Bacteria are, for this reason, designated 

 as schizomycetes or fission-fungi. 



The multiplication, or actual increase in number, of 

 bacteria always results by the process of division whereby 

 one cell forms two, and only two, new cells. There are 

 instances, as will presently be seen, where apparently one 

 cell gives rise to four or to eight cells, but in all such cases 

 the division is consecutive and not direct. That is to say, 

 the cell does not divide directly into fourths or eighths, but 

 does form two halves which, subsequently dividing, yield 

 four cells, and the next division yields eight cells. 



Cell-division among unicellular plants and animals is 

 completed in a very short length of time. This, perhaps, 

 is especially true of the bacteria. Given a suitable soil, 

 the rapidity of growth and multiplication of bacteria will 

 depend upon the temperature. The nearer the temperature 

 approaches the freezing point the slower will be the rate of 

 multiplication. On the other hand a temperature of 30° to 

 37° gives the most rapid growth. Under such conditions 

 the average bacterial cell will probably divide in less than 

 a half an hour. This rate of multiplication cannot be main- 

 tained for any length of time, owing to the exhaustion of the 

 soil and above all to the accumulation of waste products 



