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tenths of the population might have been attacked in the summer with a mild type of influenza and thus
have been protected; while in the autumn the remaining one-tenth may have suffered from the more
severe type then prevalent, with the result that the autumn mortality might even exceed that of the
summer.
The important question was raised at the time of the summer epidemic as to the extent to which
underground and above ground employees of the London Electric Railways were attacked, and I am
indebted to Mr. Blain, Operating Manager of the London Electric Railways Company, for sickness
rates in the two categories of employment.
The only statistical comparison it is possible to make is between two populations partially corrected
for sex only, one consisting largely of workers underground and the other of above ground workers in the
company's omnibus service. The ratio of sickness in these two populations is not greatly affected by
the epidemic, although there is some excess in the sickness rate among above ground employees. There
are, however, certain differences as to age, length of service, and method of selection for special duties,
which would have to be ascertained and allowed for before deductions based upon comparison of the
sickness rates in the two services could justifiably be drawn.
The sickness rates shown in the Company's figures at the height of the epidemic are much the
same as those recorded in the Metropolitan Police Force and in the London Fire Brigade.
Infection from person to person may fail to occur, for it is clear from the figures relating
to school incidence that large sections of the population are in varying degrees naturally immune. Indeed,
experiments show that persons who have escaped during an epidemic have not become infected by
deliberate association with influenza patients. No doubt almost any natural immunity can be broken
down by sufficiently prolonged exposure, as would appear from the high percentage of attacks recorded
on transport ships, amounting, it has been stated, to as much as 80 per cent, of the troops carried.
While in some households the disease has passed some members of the family and only affected the
rest with a "influenzal" cold, in others the whole family has been fatally attacked in the course of a few
days. In considering family incidence the possibility of there being an influenzal diathesis similar to that
noted in the case of tuberculosis must, of course, not be lost sight of.
In view of the great variations of case mortality at different times and in different localities, it
might, perhaps, be held by some that, in the light of more complete knowledge, it may transpire that
the cycle of existence of some lowly form of life, inert at one time and at another highly pathogenic,
is dependent upon the presence of some substance of vital origin, and on such a theory the exhaustion
of the latter would bring the epidemic to a close.
Epidemic influenza was beyond a doubt already present among troops in France in April,
but its movements there are not clear. It will, moreover, be remembered that during April many cases
of obscure illness were reported in London which there was reason to associate with influenza, so that
apparently some latent infection was already in circulation here, and indeed in many European cities,
before epidemic influenza was reported prevalent. An hypothesis which may possibly account for the
facts, in a measure, is that such latent infection remains more or less dormant until certain conditions
arise favouring its development.
Reference to abnormal weather conditions is found in almost all records of earlier epidemics.
In the 10th report of the Registrar-General (p. xxvii) a description is given of the conditions which
preceded and were thought to account for the epidemic of November and December, 1847. In the same
report details of epidemics recorded since 1728 are given (p. xxxv.), frequent reference being made to
exceptional weather conditions. Dr. Parsons reviews the meteorological records in various localities
preceding and during the prevalence of influenza in 1889-90 and concludes " there is no evidence that
the epidemic was associated with any particular kind of weather." (Report to Local Government Board
on the Influenza epidemic of 1889-90 by Dr. Parsons. 1891. d. 821
The weather records for 1918 of England and Wales are epitomized in the following abstracts from
the monthly reports of the Meteorological Office:—
Monthly weather, 1918.
January First part wintry, with snow and severe frost: second part spring-like.
February ... ... Abnormally mild: little snow and frost: rainy in North and West.
March ... ... Temperature above the normal: rainfall below it.
April Temperature below normal: wet in South and East: many dull days.
May ... ... Cold at first, then wann: severe thunderstorms and destructive hail.
June Plentiful sunshine but nights cold: rainfall deficient.
July Sunshine plentiful but rainfall excessive.
August Warm, dry and moderately sunny.
September ... Abnormally wet and very cold. n
October ... ... Dull, damp and sunless.
November... ... Damp, misty, foggy.
December ... Many rainy days and abnormally mild.
In January, 1919, the weather was generally dull and wet and in February an easterly type of
weather was predominant. In March, cold and wet weather prevailed.
No identical conditions of excess or deficiency in the principal meteorological elements appear to
mark the periods of epidemic.
An examination of the meteorological records and particularly of barometric readings for different
localities, shows that the epidemics were preceded by a noticeable fall in pressure. The fall which
preceded the autumn epidemic was far more prolonged and general than that of the summer, as also was
the epidemic which followed. The winter epidemic was preceded by a depression early in January, well
50219 I
Incidence in
relation to
exposure to
infection.