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and we only know them, as we know most things, by their
effects. There are, however, very strong reasons for believing
that the causes of all infectious diseases are specific
living organisms which find their way into the body from
without (usually from some person already suffering),
multiply within the body, and according to their individual
natures and tendencies, affect certain tissues, and so induce
characteristic symptoms. There is no reasonable cause for
doubt that influenza is a disease of this kind, and that
persons suffering from it are capable of conveying it from
one place to another, and are centres of contagion. At the
same time it is certain that the poison diffuses itself widely
in the atmosphere, and that in this sense those who are
suffering from the disease often impart it indirectly only.
It has been held both abroad and in this country, that
the present disease is not true influenza. This doubt as to
its identity is probably due to two causes : first, that few
medical men had ever seen influenza before the arrival of
the present epidemic; and second, that the habit which
has prevailed for many years past of dignifying every
attack of snivels as influenza, or an influenza cold, has led
the public to believe that the true influenza is simply a
catarrhal affection of the air passages. The last large
epidemic of influenza occurred in this country in the winter
of 1847-48. There was probably a smaller and more limited
outbreak in 1857. The former occurred when I was a
medical student, and I saw nothing of it. The latter certainly
did not prevail in London ; at any rate, though I was
in practice at the time, I saw nothing of it.
The chief symptoms of Influenza are: coldness along