How Science Helps the Body 163 



saw diphtheria in the old days and have read 

 the sinister story of the early statistics. 



But the antitoxin of diphtheria is also of 

 the greatest value in the prevention of the 

 disease among those who have been exposed 

 to infection in families, schools, and elsewhere. 



The immunity which the child secures 

 through the diphtheria which it survives, is 

 won at great cost and risk. It is called active 

 immunity. Through it the body cells have 

 adapted themselves to a new unfavorable 

 environment. On the other hand, the im- 

 munity conferred upon the child by the anti- 

 toxin which the horse manufactures, is called 

 passive immunity. The effect is immediate 

 and quite under control. But the protection 

 is short-lived and the body soon eliminates 

 the foreign agent from its blood and tissues. 

 The antitoxin does not destroy the diphtheria 

 bacilli. The body cells take care of them as 

 soon as the blight of the poison is effaced. 



In similar fashion valuable curative anti- 

 toxins are made for cerebro-spinal meningitis 

 and for tetanus, and, though less successful, 

 for a few other infections. 



