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among those living in a locality, the soil of which is more or less
polluted with sewage, it is by no means surprising that in the
conflict for supremacy which takes place between the individual
and the bacillus, the latter should frequently gain the upper
hand.
Although, therefore, it would not be accurate to say that
sewage-polluted soil caused, or could have caused, the diphtheria
prevalence, yet, given the initial presence of the diphtheria
bacillus—and near London it would be difficult to exclude it
altogether—it is obvious that such a condition must in time render
the locality a favoured spot for the disease, since it produces
conditions which are favourable for the reception of its microorganism,
its multiplication, and the development of its most
vigorous properties.
In consequence of recent researches, the view taken now by
the best authorities, is that diphtheria is not a "filth" disease as
was once so commonly thought; that is, that the presence of
unsanitary conditions, such as bad drainage, accumulations of
filth, dampness, or offensive nuisances, cannot actually cause
diphtheria, provided that the specific bacillus is absent.
Evidence is constantly accumulating, which tends to prove
this in regard to diphtheria, as well as most infectious disorders;
but this evidence also points to the conclusion that there must
be some other factors, besides the presence of bacilli, which
determine whether an individual is attacked with such diseases
or not; otherwise, infectious disorders would be much more
universally prevalent.
Briefly stated, the most important factor is what is called the
susceptibility of the individual, and probably the most potent
agents which influence this susceptibility, are the healthy or
unhealthy conditions under which the individual lives.
Although, then, the opinion now prevails that "smells,"
"bad drains," and so forth, cannot cause diphtheria, or, probably,
any infectious disease, as was once firmly believed, yet such