2SO BACTERIA, YEASTS, AND MOLDS 



as vaccination. This method has been in use over a 

 hundred years, but there is a vast deal of misunderstand- 

 ing in regard to it. The fact of the case is that 

 vaccination gives to the individual a certain amount of 

 protection against the dreaded and frequently fatal dis- 

 ease, the protection being due to about the same cause 

 as that which produces the immunity following recovery 

 from germ diseases. The protection is not an absolute 

 one, since vaccinated persons do occasionally take the 

 disease. But for a time after vaccination one is almost 

 surely protected against smallpox. How long this protec- 

 tion may last no one knows. It certainly does not last 

 forever, and if one wishes to remain immune it is neces- 

 sary to repeat the vaccination occasionally. For a year or 

 two after vaccination the protection is strong and nearly 

 absolute. But after a couple of years it gradually becomes 

 reduced, and after ten or fifteen years the amount of 

 protection afforded is very slight. The proper method, 

 therefore, of guarding against smallpox is vaccination in 

 childhood, followed by vaccination some years later, and 

 perhaps again at intervals in later life. Experience has 

 shown over and over again that proper attention to vacci- 

 nation will check smallpox epidemics, and no other means 

 has hitherto been satisfactory.. 



It rnust be recognized, however, that vaccination is not 

 always harmless. In the vast majority of cases the per- 

 son suffers nothing except a very trifling inconvenience 

 from the treatment. In extremely rare cases, perhaps, 

 more serious results arise. If these secondary troubles 

 do occur, they are usually not due directly to the vaccina- 

 tion but to the vaccination wound becoming contaminated 



