678 SUPPLEMENTARY APPENDIX. 



Value of Vaccination. 



We have not disregarded the arguments adduced for the purpose of 

 showing that a belief in vaccination is unsupported by a just view of the 

 facts. We have endeavoured to give full weight to them. Having done so, 

 it has appeared to us impossible to resist the conclusion that vaccination 

 has a protective effect in relation to small-pox. 



We think : 



1. That it diminishes the liability to be attacked by the disease. 



2. That it modifies the character of the disease, and renders it 



() less fatal, and (6) of a milder or less severe type. 



3. That the protection it affords against attacks of the disease is 



greatest during the years immediately succeeding the operation 

 of vaccination. It is impossible to fix with precision the 

 length of this period of highest protection. Though not in 

 all cases the same, if a period is to be fixed, it might, we think, 

 fairly be said to cover in general a period of nine or ten years. 



4. That after the lapse of the period of highest protective potency, 



the efficacy of vaccination to protect against attack rapidly 

 diminishes, but that it is still considerable in the next quin- 

 quennium, and possibly never altogether ceases. 



5. That its power to modify the character of the disease is also 



greatest in the period in which its power to protect from 

 attacks is greatest ; but that its power thus to modify the 

 disease does not diminish as rapidly as its protective influence 

 against attacks, and its efficacy during the later periods of life 

 to modify the disease is still very considerable. 



6. That re -vaccination restores the protection which lapse of time 



has diminished; but the evidence shows that this protection 

 again diminishes, and that, to ensure the highest degree of 

 protection which vaccination can give, the operation should be 

 at intervals repeated. 



7. That the beneficial effects of vaccination are most experienced 



by those in whose case it has been most thorough. We think 

 it may fairly be concluded that where the vaccine matter is 

 inserted in three or four places, it is more effectual than 

 when introduced into one or two places only and that if the 

 vaccination marks are of an area of half a square inch, they 

 indicate a better state of protection than if their area be at all 

 considerably below this. 



Question of Specific Protection or of Antagonism. 

 When an attack of disease secures immunity or protection against 

 another attack of disease, the two attacks are, as a rule, attacks of the 

 same disease. Some pathologists have, it is true, of late years been led to 

 suppose that one disease may confer some degree of immunity or protec- 

 tion against another different disease ; but instances of this are few, and r 

 moreover, cannot be regarded as thoroughly established. The ordinary 

 instances of immunity are so clearly those in which the attack, natural or 



