164 The Story of the Bacteria 



Of course the eager workers in the labora- 

 tories have tried to get antitoxins for many 

 other of the bacterial diseases. But somehow 

 the method did not seem to work so well in all. 

 There are many obvious reasons why this 

 should be, but they are too complex to con- 

 sider here. There is little doubt that as 

 research goes on still further discoveries will 

 be made of effective antitoxins. 



In the meantime, however, the student of 

 bacterial diseases has turned to other phases 

 of the protective mechanism. Active im- 

 munity can be secured in other ways than by 

 the weathering of an infection. Thus it has 

 been found that if a mass of disease-inducing 

 bacteria, from an artificial culture, be killed 

 by heat and portions of these be introduced 

 into the body, its cells gradually adapt them- 

 selves to the poisons which the dead bacteria 

 contain, so that the body is in a measure 

 protected from an attack of the disease of 

 which they are the regular incitants. 



Thus with typhoid fever, Asiatic cholera, 

 and plague, important practical results have 

 been secured. The persons thus forearmed 



