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activate various secondary or associated organisms, pneumococci, streptococci,raeningo-cocci,
etc.
In the pandemic, young vigorously multiplying spores are presumably the
agencies concerned in favouring the wide and rapid dissemination through the then
highly susceptible community; whereas, in the trailers, following Upon the
immunising reaction induced in the community by the "shock attack," the epidemic
influence seems constrained to ally itself with facultative parasites of the human
body, and there results a less rapidly spreading, though for a time at any rate a
still very fatal form of epidemic disease.
The suggestion has been made that the change from pandemic phase to trailer
phase is bound up with "mutation" of the influenza germ; this change may also
be attributable in part to substitution for the process of multiplication by young
and vigorous spores of multiplication by "resting" spores. It may be conjectured
that, in the trailers near the pandemic, the two types of spores are commonly met
with in association. As the distance o time from the pandemic prevalence increases,
however, spores of a "resting" type perchance assume the ascendency, and then
at a period still more remote, the characteristically pandemic type of spore formation
may again begin to predominate.
On such assumptions the post-pandemic trailers might be expected gradually
to become less fatal and less frequent; in the trough between two pandemics the
organisms would be comparatively feeble and trailers of a mild type might be
expected then to occur at prolonged intervals of time; finally, as the appointed
occurrence of the pandemic phase again approached the trailers would tend to
occur more frequently and gradually assume greater severity.
This scheme of things may be further illustrated as follows: The "primary
influence" concerned in producing influenza, following upon biological change,
which it has been assumed occurs towards the close of a pandemic period, obviously
begins to contend with difficulty in spreading through the increasingly immunised
community; it thus resembles a car which has been moving rapidly on high gear
and now has to drop into low gear and move more slowly. After 10 or 15 years
travelling along this upward ascent (during which time the extent of immunization
of the population as a whole, against the various manifestations of influenza, is
steadily growing) the climb gradually begins to lessen in severity; but for another
10 or 15 years (during which the susceptibility of the population slowly increases)
the journey has still to continue on low gear. Then as the community, owing to
the comparative infrequency of prevalence of one or other of the diseases of the
influenzal group, becomes more and more susceptible the rapidity of transference
of infection shows increase and, when the time for pandemic prevalence again
arrives, change into high gear is once more effected and world-wide spread of
influenza in pandemic phase again results.
This comparison is not so fantastic as might at first sight appear. There
is good reason in fact for claiming, as has been elsewhere explained, that influenza
is due to a "primary influence" and to associated "satellite influences." The
bringing into operation of one and another "satellite influence" must materially
affect the epidemiological manifestations of the postulated "primary influence."
The appeal to satellite influences is, moreover, suggested by the need for explaining
the relation of the influenzal group of diseases to pandemic influenza itself.
In the opening sentences of his great chapter on " Influenzas and Epidemic
Agues," Creighton laid the foundations of the modern epidemiological theory on
this subject. He says: "Epidemic agues are found in the same chapter with
influenzas for the reason that they can hardly be separated in the early part of the
history " there are periods, such as 1657-59, 1678-79 and 1727-29, when
short waves of epidemic catarrhs or catarrhal fevers came in the midst of longer
waves of epidemic agues, ' hot agues ' or intermittents, the whole being called by
the people the ' new disease ' or the ' new ague,' while by physicians, such as
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