ESSAYS ON BACTERIOLOGY. 107 



ten years of a successful vaccination. This is com- 

 ing to be accepted throughout the world as the basis 

 for the regulation of re-vaccination. If all children 

 were vaccinated within the first and at the tenth year 

 of life, smallpox would be practically abolished, as in- 

 deed it has been from those communities in which this 

 rule is followed. 



Third, we should expect the thoroughness of the 

 vaccination to stand in something like a direct ratio to 

 the degree of protection. And this we certainly find 

 to be true. The experience in every outbreak of 

 smallpox confirms this rule. And the lesson of it is 

 obvious: we should vaccinate thoroughly, knowing 

 "that the result will be a proportionate thoroughness of 

 protection. We wrong those who commit this mat- 

 ter to our care, and wrong the public, by failure to 

 appreciate and act upon .this too much neglected 

 truth. 



Fourth, the protection afforded by vaccination is a 

 positive, an active thing; it is an endowment with a 

 new power, conferred upon the individual and to be 

 obtained, so far as we know, only in this way. He 

 who has not had variola is susceptible to that disease 

 unless properly vaccinated. And that vaccination 

 should be genuine. 



The protection comes, not by the scarification and 

 its resulting lesion, not by the scarification and the 

 application of vaccine lymph; but by the successful 

 induction of the specific lesions of vaccinia, and the 



