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what it may, can only find congenial conditions for
its full development in damp and impure air.
The theory of Pettenkofer is that the essential
conditions for the active manifestations of the disease
are a porous soil, charged with excrementitious
matter, and having a certain degree of hydration,
as happens when the subsoil water has been
just drawn off or is slowly retiring. All these conditions
were singularly coincident with the localisation
of the disease in the eastern districts of London;
for the soil is gravelly and therefore very
porous to air and water, and it is largely charged
with excrementitious matters derived from the
local tide-locked sewers. It is also remarkable
that for some months before the outbreak of the
disease, the subsoil water had been gradually sinking
in consequence of the drainage operations that
were necessary for the construction of the main
low-level sewer, and its branch to the Isle of Dogs.
Now according to Pettenkofer, it is exactly under
these circumstances that a district is most liable
to choleraic infection.
Another theory which has been advanced to account
for the local character of the outbreak is, that
the water distributed to the infected districts was
charged with choleraic matter; but looking at all
the facts of the case, it is clearly evident that while