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in the bud. Since its discovery in the nineties of the last century,
anti-diphtheritic serum has lowered the case mortality rate from over
30 per cent. to under 8 per cent.—a Godsend to humanity. But this
serum, it should be noted, is used for treatment. Is there no prevention
at all ? Assuredly, yes ! Before I explain, I must give a short statement
as to the meaning of Susceptibility and Immunity.
If I say I am immune to a disease I mean that I am not susceptible
—not liable to contract that disease. Immunity may be possessed by
an animal naturally and it is then called natural immunity; for example,
man is immune to swine plague, a disease that affects the lower animals.
Similarly, whereas man may suffer from typhoid fever or cholera, the
lower animals never so suffer, they are immune or non-susceptible to
the germ of infection of typhoid and cholera. In addition to natural
immunity there is another form called Acquired Immunity. We
develop acquired immunity by suffering from an attack of the disease,
or we can obtain acquired immunity by means of inoculation against
that disease. Do not misunderstand me ; one attack of smallpox or of
typhoid or of scarlet fever confers immunity either for life or for a
great many years; but in the case of erysipelas, diphtheria, influenza
or pneumonia, unfortunately the immunity acquired is of brief duration
and one may have several attacks of these diseases. Now why is it
that the child between 2 and 6 years is so susceptible to Diphtheria,
and what is it that produces immunity in later years ? It is universally
recognised that immunity to Diphtheria is anti-toxin immunity; in
other words, the immune person must have sufficient anti-toxin
circulating in his tissue fluids to neutralise the Diphtheria toxins that
enter his system from the vitality of Diphtheria germs which have got
into some part of his throat or nose. A person with sufficient anti-toxin
in his blood is armed with all the defences necessary to repel an attack
of Diphtheria. Where do I get the anti-toxin which is circulating in
my blood and which has made me immune, that is not susceptible, to
the Diphtheria germ which people cough into my face, my nose and
throat every week ? My anti-toxin is manufactured in my tissue cells;
these cells have produced the anti-toxin because, again and again, they
have been stimulated by the poisons or toxins given off by a scanty
infection of the Diphtheria germ which I have received unwittingly,
without knowing, from time to time. Nature, if left to herself,
takes some considerable time to establish this immunity and there are