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51
actual cases, swabbing of contacts and the search for carriers. At
the onset of an outbreak this method may prove successful in
cutting it short, at any rate for a time, but when the cases are
distributed throughout a school or are in different schools, the
number in which diphtheria bacilli are found in the throats is so
oreat, that isolation of all suspected cases is impossible. Our
best method of success is by raising the herd immunity of the
community. The problem is to render the susceptible, insusceptible.
In the last annual report of the Ministry of Health, Sir George
Newman states that in the case of Diphtheria this is not only feasible
and practicable but eminently desirable.
As far as this district is concerned Schick-testing and active
immunization' are inovations, and it may be advisable to give a
short account of the process. The Schick-test of susceptibility was
introduced in 1913 and involves the injection into the skin of a
minute dose of Diphtheria toxin diluted with saline solution. The
reaction depends on the local irritant action of Diphtheria toxin
when so injected. If the blood of the person injected contains an
insufficient amount of anti-toxin to protect him against Diphtheria,
he is liable to contract the disease if he comes in contact with
another person suffering from Diphtheria. In this case he will give
what is called a positive reaction. This reaction is characterised
by an area of redness about half &n* inch or more around the site
of injection. If the person tested is immune or not susceptible to
diphtheria, no redness occurs and he is said to be a negative reactor.
The next step is the active immunisation of the susceptible
persons or the positive reactors. Passive immunity is frequently
brought about by injecting small doses of anti-toxin and this is
made use of to protect children in a general hospital exposed to
infection when Diphtheria occurs in a ward. Doctors also give
doses of anti-toxin to other members of the family when a case has
occurred in a house. This kind of immunity is called passive
because the cells of the blood do not produce any anti-toxin, but
the anti-toxin is introduced from without and circulates in the
blood. The immunity thus conferred is transient and probably lasts
only for a few weeks.
Active and prolonged immunity can only be conferred when
the cells of the body manufacture anti-toxin, and this form of
immunity is produced when a person suffers from the disease. This
is the reason why a person rarely suffers more than once from such
diseases as Measles, Scarlet Fever, Diphtheria, etc. The patient
tas stored in his tissues sufficient anti-body to fight the particular
disease for the rest of his life. The same process can be introduced