Page:Popular Science Monthly Volume 23.djvu/668

650, lamps are extinguished by the accumulation of their dead bodies. Every fire, therefore, whether in-doors or out, is a sort of mosquito hades. In some tropical countries, despite heat of climate, fires are kept up all night in every apartment as a preventive against fevers; and experience has demonstrated that they are more effective when placed between the open window (or door) and the body of the person to be protected. In this way it is easy to comprehend how every mosquito will fly directly into the light and the fire before reaching the thus protected sleeper.

15. "The air of cities in some way renders the poison innocuous, for, though a malarial disease may be raging outside, it does not penetrate far into the interior."

In conformity with this statement, we may easily conceive that mosquitoes, while invading cities during their nocturnal pilgrimages, will be so far arrested by walls and houses, as well as attracted by the lights in the windows and streets of the suburbs, as that many of them will in this way be prevented from penetrating far "into their interior." Even a single row of houses, on one side of a road, with its contiguous fences, lamps, and closely-knit hedge-rows, may so far completely obstruct the onward flight of mosquitoes coming from some neighboring swamp as to prevent their crossing the street. The curious instances in which people living on one side of a road are attacked with ague, while those living on the other side escape, as on the high-road between Chatham and Feversham (see Macculloch on "Malaria," p. 121), and in Cività Vecchia (see Johnson on "Tropical Climates," p. 315), are quite as susceptible of possible explanation by the mosquito theory as by the marsh-vapor conception, for that the infected air from the marshes does not cross the street is inconceivable.

16. "Malarial diseases are most prevalent toward the latter part of summer and in the autumn."

It has been already explained in what manner—and the fact is a common observation—mosquitoes are more numerous also during the later summer and autumn months.

17. Malaria is arrested, not only by trees, walls, etc., but also by canvas curtains, gauze veils, and mosquito-nets.

Sir Francis Day (p. 87) tells us that travelers, besides being warned against night and morning temperature, should be instructed at night to employ mosquito-curtains "through which malaria can seldom or never pass."

Dr. Macculloch (pp. 137, 138) says that, by surrounding the head with a gauze veil or conopeum, the action of malaria is prevented, and that thus it is possible even to sleep in the most pernicious parts of Italy without hazard of fever. The prophylactic efficacy of fine cloth or gauze at night is further attested by Dr. Johnson ("Tropical Climates," pp. 316, 317), as quoted on p. 318 of La Roche's well-known