On the Hackensack marshes to-day trenches are cut to let the water out of the tidal pools; while in low-lying areas, which cannot be thus drained, the central lowest spot is selected, a barrel is sunk at this spot, and four or five "killie" fish are placed in it. Trenches are cut converging into this barrel from the whole of the area to be drained, and behold, no more mosquitoes can breed in that area, and, in the language of the day, "get away with it." Finally, most consoling of all, it was discovered that, while the ordinary _Culex_ mosquito can breed, going through all the stages from the egg to the complete insect, in about fourteen days, so that any puddle which will remain wet for that length of time, or even such exceedingly temporary collections of water as the rain caught in a tomato-can, in an old rubber boot, in broken crockery, etc., will serve her for a breeding-place, the _Anopheles_ on the other hand takes nearly three months for the completion of her development. So that, while a region might be simply swarming with ordinary mosquitoes, it would frequently be found that the only places which fulfilled all the requirements for breeding-homes for the _Anopheles_, that is, isolation from running water or larger streams, absence of fish, and persistence for at least three months continuously, would not exceed five or six to the square mile. Drain, fill up, or kerosene these puddles,--for they are often little more than that,--and you put a stop to the malarial infection of that particular region. Incredible as it may seem, places in such a hotbed of fevers as the west coast of Africa, which have been thoroughly investigated, drained, and cleaned up by mosquito-brigades, have actually been freed from further attacks of fever by draining and filling not to exceed twenty or thirty of these breeding-pools.