At The Rio Magdalena The Frequency Of Mosquitos Is Regarded As Troublesome, But Salutary.

These animals, say the inhabitants, give us slight bleedings, and preserve us, in a country excessively hot, from the scarlet fever, and other inflammatory diseases.

But at the Orinoco, the banks of which are very insalubrious, the sick blame the mosquitos for all their sufferings. It is unnecessary to refute the fallacy of the popular belief that the action of the mosquitos is salutary by its local bleedings. In Europe the inhabitants of marshy countries are not ignorant that the insects irritate the epidermis, and stimulate its functions by the venom which they deposit in the wounds they make. Far from diminishing the inflammatory state of the skin, the stings increase it.

The frequency of gnats and mosquitos characterises unhealthy climates only so far as the development and multiplication of these insects depend on the same causes that give rise to miasmata. These noxious animals love a fertile soil covered with plants, stagnant waters, and a humid air never agitated by the wind; they prefer to an open country those shades, that softened day, that tempered degree of light, heat, and moisture which, while it favours the action of chemical affinities, accelerates the putrefaction of organised substances. May not the mosquitos themselves increase the insalubrity of the atmosphere? When we reflect that to the height of three or four toises a cubic foot of air is often peopled by a million of winged insects,* (* It is sufficient to mention, that the cubic foot contains 2,985,984 cubic lines.) which contain a caustic and venomous liquid; when we recollect that several species of culex are 1.8 lines long from the head to the extremity of the corslet (without reckoning the legs); lastly, when we consider that in this swarm of mosquitos and gnats, diffused in the atmosphere like smoke, there is a great number of dead insects raised by the force of the ascending air, or by that of the lateral currents which are caused by the unequal heating of the soil, we are led to inquire whether the presence of so many animal substances in the air must not occasion particular miasmata.

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