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78
1899]
upon diphtheria patients without any illness on their part. To
exhaust the etiology of an infectious disease like Diphtheria, we
require,—adopting the phraseology of the old scholastic logicians,—
to know not only the causa causans of the disease (that is the specific
micro-organism) but also the causa efficiens and the causa movcns, which
must be present in order that the disease may become widely prevalent.
To use a simple illustration. A drunken man is thrown by
a restive horse, and dies from a broken and dislocated neck. The
cause of death may with accuracy be ascribed to the man's drunkenness,
to the restiveness of the horse, or to the fractured and dislocated
vertebra. Properly it is ascribed to the conjunction of all
these circumstances. A neglect to consider any one of these
factors will give a distorted and imperfect view of the cause of the
accident and its fatal issue. So it is with infectious diseases, and
especially Diphtheria, in which the element of personal predisposition
and of environment is so marked. The bacteriological
study of Diphtheria, far from being the negation of traditional
etiology, is but the logical outcome of it; and secondary causes
still maintain their traditional value as the indispensable concomitants
of the Klebs-Lœffler bacillus. The causa efficiens and the
causa movens consist of the combined favouring influence of personal
constitutions and conditions of environment, which Colin has
named le melien épidémique."
Now and again, when the external conditions are favourable
to Diphtheria, there is no outbreak of the disease, while on the
other hand though the season be wet an occasional outbreak may
arise from personal infection in a crowded school or in a densely
populated district, " but," to again quote Dr. Newsholme, " this
does not controvert or deprive the statement here advanced that
the chief efficient and motive cause of epidemics, and still more of
pandemics, of diphtheria is the occurrence of a series of dry years,
giving rise to conditions which favour the multiplication and probably
at the same time increase the virulence of the diphtheria
bacillus."
Before leaving this question of the influence of rainfall I would
remark that Dr. Newsholme, as indeed I have myself done, noticed
that, if a heavy rainfall, accompanied with a low barometer,