650 THE POPULAR SCIENCE MONTHLY. 



nierous, 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 pene- 

 trate 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 inte- 

 rior." 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 at- 

 tacked with ague, while those living on the other side escape, as on the 

 high-road between Chatham and Feversham (see Macculloch on " Ma- 

 laria," p. 121), and in Civita Vecchia (see Johnson on "Tropical Cli- 

 mates," 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 incon- 

 ceivable. 



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. 31G, 317), as quoted on p. 318 of La Roche's well-known 



