Unfortunately, one is never sure of arriving at such a result, and no one
can say, _a priori_, whether the forced cultivation of a given malarious
tract will render it healthful. It must always be remembered that the
first effect of forced cultivation, which requires an overturning of the
soil by means of the plow, the spade, and the pick, is an unfortunate one,
from a hygienic point of view, whenever we have to deal with a malarious
country. Experience has shown, especially in Italy and America, that this
overturning of the soil almost invariably increases the local production
of malaria. And this can be readily understood, since the plowing and the
digging in a soil containing the specific ferment increase the extent of
surface of the ground in immediate contact with the atmosphere. This first
mischievous effect is often gradually weakened by the continued
cultivation, and may end by disappearing. At other times, on the contrary,
it persists obstinately, and one is often forced in desperation to the
resolve to level the ground again and to varnish it, so to speak, with a
thick sowing of grass, if he wishes to suspend or weaken the malarial
production.
However, when the local conditions will permit, it is well to try whether,
by means of forced cultivation of the soil, it may not be possible to
increase the efficacy of the hydraulic method of procuring immunity from
malaria, or of the hydraulico-atmospheric method of "overlaying.
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