"2d. It is almost never developed at a lower temperature than 60° Fahrenheit.
"3d. Its evolution or active agency is checked by a temperature of 32°.
"4th. It is most abundant and most virulent as we approach the equator and the sea-coast.
"5th. It has an affinity for dense foliage, which has the power of accumulating it, when lying in the course of winds blowing from malarious localities.
"6th. Forests, or even woods, have the power of obstructing and preventing its transmission, under these circumstances.
"7th. By atmospheric currents it is capable of being transported to considerable distances—probably as far as five miles.
"8th. It may be developed, in previously healthy places, by turning up the soil; as in making excavations for foundations of houses, tracks for railroads, and beds for canals.
"9th. In certain cases it seems to be attracted and absorbed by bodies of water lying in the course of such winds as waft it from the miasmatic source.
"10th. Experience alone can enable us to decide as to the presence or absence of malaria, in any given locality.
"11th. In proportion as countries, previously malarious, are cleared up and thickly settled, periodical fevers disappear—in many instances to be replaced by the typhoid or typhus."