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The reason of this is that social status determines the exposure
to the virus of the disease. It is very interesting to note that a
large percentage of cases who have previously suffered from
diphtheria give positive Schick reactions. The anti-toxin administered
apparently prevents or at least does not encourage the
acquisition of a lasting immunity.
Artificial Active Immunisation.—When it has been determined
that the person tested is susceptible, steps can be taken to induce
an artificial active immunity. The term "active" is used to
contrast the process with artificial "passive" immunity which is
induced by the injection of the specific anti-toxin.
Passive immunity lasts but a short time, 3 to 4 weeks, whereas
the active immunity induced by artificial means lasts more or less
throughout life.
Park of New York and his collaborators have experimented
since 1913 with an anti-toxin mixture of the diphtheria bacillus.
He found that a suitable amount of diphtheria toxin neutralised to
a certain extent with anti-toxin will induce in susceptible persons an
active immunity of a lasting character. A standard toxin has been
evolved as a result of careful and exact experiments.
The dose of this mixture is injected into the person at a
convenient site under the skin, usually of the arm. Three injections
are given at intervals of 8 to 15 days.
As a result of the injection an inflammatory reaction occurs,
characterised by a slight swelling, redness and slight pain at the
site of injection. All these symptoms, however, disappear rapidly
and in only a few rare individuals do general symptoms of fever
and shivering occur. Children tolerate an anti-toxin mixture
better than adults.
A certain number of accidents have been recorded after an
injection of the toxin mixtures in America but these, it has been
pointed out, have been due to the use of products of poor quality
produced by uncontrolled firms. No untoward results have
occurred in this country.