COMBATING PARASITIC BACTERIA. 179 



which occur in periodical epidemics of so great 

 severity, as to make people in general willing to 

 submit to inoculation as a protection. A further 

 objection arises from the fact that the immunity 

 acquired is not necessarily lasting. The cattle 

 inoculated against anthrax retain their protective 

 powers for only a few months. How long similar 

 immunity might be retained in other cases we can 

 not say, but plainly this fact would effectually 

 prevent this method of protecting mankind from 

 being used except in special cases. . It is out of 

 the question to think of constant and repeated 

 inoculations against various diseases. 



As a result, the principle of inoculation as an 

 aid in preventive medicine has not proved of very 

 much value. The only other human disease in 

 which it has been attempted seriously is Asiatic 

 cholera. This disease in times of epidemics is so 

 severe and the chance of infection is so great as 

 to justify such inoculation. Several bacteriolo- 

 gists have in the last few years been trying to 

 discover a harmless method of inoculating against 

 this disease. Apparently they have succeeded, 

 for experiments in India, the home of the chol- 

 era, have been as successful as could be antici- 

 pated. Bacteriological science has now in its 

 possession a means of inoculation against chol- 

 era which is perhaps as efficacious as vaccination 

 is against smallpox. Whether it will ever be used 

 to any extent is doubtful, since, as already pointed 

 out, we are in a position to avoid cholera epidemics 

 by other means. If we can protect our commu- 

 nities by guarding the water supply, it is not 

 likely that the method of inoculation will ever be 

 widely used. 



Another instance of the application of pre- 



