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risk of attack than ever before in its history. In this district the results
obtained, though satisfactory, were not outstanding. Sufficient children
are now immune to remove the risk of any substantial outbreak. Probably
sufficient school children are immune to render unnecessary any
special effort being directed towards any more being done, the time
being better devoted to those under five years of age and still more so
to the child of one year.
Some hope that improved sanitation, greater attention to food,
and the other factors which improve environmental hygiene will result
in a lowering of infection. Possibly in time factors will be discovered
which can modify man's susceptibility to attacks by micro-organisms.
Until then, it must be accepted that there will remain the interplay and
interaction between the parasite and the human host until such time
as the organism has adapted itself to a symbiotic existence, no longer
being pathogenic to man. As long as the organism remains pathogenic
and also prevalent, an individual will need to be actively protected
against attack. If the organism disappears and if the reaction it causes
to the human which it attacks is so intense that control of the individual
is easy, then immunization as a routine is unnecessary. This is to-day's
position in this country in regard to smallpox and vaccination against it.