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place in the winter of 1891-92, and after a minor recrudescence
in the spring of 1893, a fifth prevalence on a wide scale took
place in the winter of 1893-94. England is now passing through
a sixth epidemic period. Two detailed reports have been issued
by the Board on the subject. The first was Dr. Parsons, "On
the Influenza Epidemic of 1889-90," with an introduction by Sir
George Buchanan, M.D., F.R.S., the Board's Medical Officer
at that date. The second was a "Further Report on Epidemic
Influenza, 1889-92," by Dr. Parsons, with papers on the Clinical
and Pathological aspects of the Disease, by Dr. Klein, F.R.S.,
and an introduction by myself.
A "Provisional Memorandum upon Precautions advisable
at times when Epidemic Influenza threatens, or is prevalent,"
was also drawn up by me in January, 1892, and was issued by
the Board to local sanitary authorities.
The further study made by the Medical Department as to
the natural history of Influenza, and as to its clinical and bacteriological
characteristics, goes to show that it is a disease
against which it is most difficult to apply measures of prevention
with any substantial prospect of success.
Influenza is highly infective from person to person; its
infectious quality is often manifested before the disease is fully
recognised; its incubation period is one of the shortest of all
infectious diseases; it varies so much in intensity that many
cases are never diagnosed at all; one attack confers no marked
immunity against another; and the infection is largely eliminated
by means of the lungs, the sputa of the sick being invariably
charged, during the acute stage of the disease, with its pathognomonic
micro-organism. The disease calls primarily for measures
of isolation and of disinfection, but there are difficulties
in making any such measures universally applicable. Wherever
they can be carried out, the following precautions should, however,
be adopted:—