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79
[1899
occurred during a prolonged dry period, an outbreak of diphtheria
to a certainty followed. But this is easily explained by the circumstance
that the micro-organisms that cause diphtheria increase and
multiply in a warm soil that is free from excessive moisture. It is
not surprising, therefore, " that they should subsequently become
displaced from the soil by rainfall, or become aspirated from the
soil, when apart from rainfall the barometer falls, or the interior of
a house is at a much higher temperature than the subsoil underlying
it. The idea that micro-organisms may be displaced from
contaminated soil by means of rain may cause momentary surprise,
as the first thought would be that they would be washed into the
deeper subsoil. But this notion ignores the fact that in towns, and
even in villages, the area on which direct percolation of rainfall from
the ground level can occur is, in these days of impervious pavements
and roads, becoming rapidly diminished ; while at the same time
the entire ground under dwelling houses is in only a small minority
of instances of covered with impermeable material, or with this
material in sufficient thickness to exclude the ground air. Consequently
when rain falls there is a great lateral as well as upward
displacement of ground-air, and the rainfall in conjunction with the
simultaneous aspirating effect of a lower barometric pressure,
ensures the entry of ground air into the house."
I trust that these remarks will be carefully considered, and that
they will have a strong effect in inducing members of the Vestry,
property owners, and builders to see that it is absolutely essential
to have the surface of the ground surrounding houses made as impervious
as possible, and that no houses are permitted to be occupied
until the ground on which they stand had been solidly concreted.
This is all the more necessary since rainfall has also a very similar
effect on other diseases such as Scarlet Fever, Rheumatic Fever,
Erysipelas, and Puerperal Fever.
Among the predisposing causes must be reckoned primarily
general dampness of the soil and of the dwelling, for each by
tendering to lower the vital functions leaves the system less able to
meet the attack of the bacillus when it invades the throat. Here
again is a great reason why the surroundings of homes should be