COMBATING PARASITIC BACTERIA. 181 



very weak, but is followed later by a more powerful 

 inoculation. The result is that after a short time 

 the individual has acquired the power of resisting 

 the hydrophobia poisons. Before the incubation 

 period of the original infectious matter from the 

 bite of the rabid animal has passed, the inoculated 

 individual has so thoroughly acquired a tolerance 

 of the poison that he successfully resists the attack 

 of the infection. This method of inoculation thus 

 neutralizes the effects of the disease by anticipat- 

 ing them. 



The method of treatment of hydrophobia met 

 with extraordinarily violent opposition. For sev- 

 eral years it was regarded as a mistake. But the 

 constantly accumulating statistics from the Pas- 

 teur Institute have been so overwhelmingly on 

 one side as to quiet opposition and bring about a 

 general conviction that the method is a success. 



The method of preventive inoculation has not 

 been extensively applied to human diseases in ad- 

 dition to those mentioned. In a few cases a similar 

 method has been used to guard against diphtheria. 

 Among animals, experiment has shown that such 

 methods can quite easily be obtained, and doubt- 

 less the same would be true of mankind if it was 

 thought practical or feasible to apply them. But, 

 for reasons mentioned, this feature of preventive 

 medicine will always remain rather unimportant, 

 and will be confined to a few of the more violent 

 diseases. 



It may be well to raise the question as to why 

 a single attack with recovery conveys immunity. 

 This question is really a part of the one already 

 discussed as to the method by which the body 

 cures disease. We have seen that this is in part 

 due to the development of chemical substances 



