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27
The diagnostician must of course always have in mind the time and space relationships
of the particular sufferer under examination, and must look for such clues as
may be to hand on careful consideration of symptoms and the previous disease
history. This can be quite successfully accomplished, in some instances, for it is a
well-known fact that particular individuals are apt to react again and again to
influenza, some years after or before the occurrence of a widespread epidemic
prevalence.
From the epidemiological standpoint it is clear, then, that the epidemics affecting
the central nervous system which have been under consideration, all stand in close
relationship to one another and to influenza. They are none of them "new
diseases," though it must be agreed that in order to find parallel instances to the
recently observed vagaries of encephalitis lethargica we have to hark right away
back for a number of years. Dr. Crookshank has told us of the "Nona" of 18891890,
and of the choreas and schlafsuchts of still earlier times, and my colleague
Dr. C. J. Thomas recollects seeing cases with lethargy and ocular palsies in London
in 1899-1900.
The question has now, therefore, to be considered whether epidemics, attacking
different portions of the cerebro-spinal nervous system and therefore producing
widely differing symptom complexes, may be due to related viruses, or even to
some one virus, producing effects of varying character when operating upon communities
exhibiting differing degrees of resistance to infection, or living under
differing climatic or social conditions. Thus, at one time and in one place, the
virus more particularly affects the grey matter in the cortex or the mid-brain and,
at another time and in another place, the meninges, or the anterior cornua of the
grey matter of the spinal cord, or poisons even the nerves themselves. It would
appear, in fact, that the circle is now completed and we are back again at the starting
point—at the Heine-Medin concept, of an epidemic disease affecting one or another
part of the nervous system, which was roughed out in Scandinavia and Germany
40 or more years ago, though it must be remembered that under that conception,
while the cases occurring in the "trailers" were grouped together, the latter were
not at the same time roped in with the "pandemics" as forming part and parcel
of an influenzal constitution.
It is, at any rate, plain, in the light of recent events that no clear line of
demarcation can be drawn between epidemic cerebro-spinal meningitis and the
posterior basic meningitis of small children; between epidemic hiccough and
encephalitis lethargica; between poliomyelitis and polioencephalitis; between
the form of polioencephalitis which has been described as epidemic stupor and
encephalitis lethargica; between the various types of the above diseases encountered
in Melton Mowbray, Devon, Cornwall, London, Sweden and America. The time
seems, therefore, to be ripe for a little synthesis, now that analysis has brought
matters to this impasse.
Crookshank's reminder may be quoted here. He says: "it is only with regard
to cases (not epidemics or outbreaks) that the suggestion of a protean malady is
entertained. Yet, as a matter of fact, always in each apparently autonomous
prevalence are all 'types' represented, and for each type in each prevalence is there
somewhere some prevalence represented by predominance of that type."
Instability
of type in the
influenzal
group of
diseases and
its influence
upon the
form of the
epidemic
wave.
It is desirable to consider in the light of the foregoing considerations the present
"epidemic constitution": a subject particularly deserving of study now it is
realised that influenza, as is its wont, has been once again revealing itself, between
1917 and 1924, in quite unexpected forms.
The two extreme types of epidemic diseases—those of "stable type" (such
as measles) and those of "unstable type" (the " mobile diseases"), of which the
striking example is influenza—stand most aloof from one another in two respects:
first, as regards extent of variation in clinical symptoms, and second, in the contrasts
presented by the forms of their epidemic waves. In measles the rhythm of the