COMBATING PARASITIC BACTERIA. 175 



While it may be best that the knowledge of cura- 

 tive methods be confined largely to the medical 

 profession, it is eminently desirable that a knowl- 

 edge of all the facts bearing upon preventive 

 medicine should be distributed as widely as pos- 

 sible. One person can not satisfactorily apply 

 his knowledge of preventive medicine if his 

 neighbour is ignorant of or careless of the facts. 

 We can not hope to achieve the possibilities lying 

 along this line until there is a very wide distribu- 

 tion of knowledge. Every epidemic that sweeps 

 through our communities is a testimony to the 

 crying need of education in regard to such sim- 

 ple facts as the source of infectious material, the 

 methods of its distribution, and the means of ren- 

 dering it harmless. 



PREVENTION IN INOCULATION. 



It has long been recognised that in most cases 

 recovery from one attack of a contagious disease 

 renders an individual more or less immune against 

 a second attack. It is unusual for an individual 

 to have the same contagious disease twice. This 

 belief is certainly based upon fact, although the 

 immunity thus acquired is subject to wide varia- 

 tions. There are some diseases in which there is 

 little reason for thinking that any immunity is ac- 

 quired, as in the case of tuberculosis, while there 

 are others in which the immunity is very great 

 and very lasting, as in the case of scarlet fever. 

 Moreover, the immunity differs with individuals. 

 While some persons appear to acquire a lasting 

 immunity by recovery from a single attack, others 

 will yield to a second attack very readily. But 

 in spite of this the fact of such acquired immu- 

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