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Fig. 132.—Culex or Common Mosquito, above (possibly carries dengue fever). Anopheles or Malarial Mosquito, below (not always infected). Body of malarial mosquito is never held parallel to the supporting surface (unless a leg is missing); it has five long appendages to the head, the culex (above) has only three. (Draw.)

Fig. 133.—Protective White Corpuscle (phagocyte) digesting a microbe.

animal, see "Animal Biology," p. 7). Afterwards a spore (in another stage) may be transmitted by this mosquito when it bites another person. The germ enters a red corpuscle, grows, and finally divides into many little spores. At this moment the corpuscle itself breaks up, setting free in the blood the spores and toxin formed. This causes the chill and fever. This development usually takes forty-eight hours, hence the fever occurs every other day. These mosquitoes begin to fly at dusk. How are they recognized? (Fig. 132.) They should be kept out of houses by screens or from the beds by netting. Kerosene should be poured on breeding places at the rate of one ounce for fifteen square feet of standing water. This should be repeated twice a month. Cactus macerated in water may be used, and forms a permanent film on the water. Stagnant pools may be filled or drained (Exp. 4). Malarial patients should themselves be screened, as the chief source of danger to others; for only mosquitoes who suck the blood of malarial patients will transmit the disease. Even then it is only transmitted to those whose white blood corpuscles are unable to protect them (Fig. 133).