50 The Story of the Bacteria 



way how long it would be before somebody 

 would be trying to modify the colors of some 

 of the bacteria by the well-known horti- 

 cultural methods. His idea was a clever one, 

 but he was behind the times, for already a 

 German bacteriologist had, starting with a 

 deep purple-forming species of bacteria, and 

 selecting and replanting the lighter-colored 

 colonies, at last obtained cultures which were 

 nearly white, but were in other respects 

 essentially the same. 



In many other ways the bacteriologist can 

 modify the life processes of bacteria by suc- 

 cessive generations of selective cultures. Acid 

 producers can be restrained, or their powers 

 exalted. Lovers of oxygen can be made to 

 go without it. The fermentative and putre- 

 factive capacities of many forms can be 

 profoundly altered. They can be adapted 

 to strange foods and to outlandish con- 

 ditions. Harmful species can be rendered 

 harmless and the virulence of other forms 

 exalted. 



Thus the great and far-reaching prin- 

 ciples of natural selection, in accordance with 



