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"(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
quinquennium, 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
attack 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 period 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 has
been inserted in three or four places, it is more effectual than
when introduced into one or two plnces 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."
"434. A careful examination of the facts which have been brought
under our notice has enabled us to arrive at the conclusion that,
although some of the dangers said to attend vaccination are
undoubtedly real and not inconsiderable in gross amount, yet