646 TEE POPULAR SCIENCE MONTHLY. 



as a probable cause of malarial fever, in place of the marsb-vapors of 

 Lanscisci (" New Orleans Medical and Surgical Journal," vol. iv, 

 pp. 5G3-G01, 1848). And, even before bis time, I find tbat a paper on 

 tbe " Mosquital Origin of Malarial Disease " was publisbed by Dr. Jobn 

 Crawford in a periodical known as tbe " Baltimore Observer," 1807, 

 no copy of wbicb I bave yet been able to get bold of. 



I now propose to present a series of facts some of tbe best known 

 and most generally establisbed facts witb regard to the so-called 

 " malaria] poison," and to sbow bow they may be explicable by the 

 supposition that the mosquito is the real source of disease, rather than 

 the inhalation or cutaneous absorption of a marsh-vapor. These facts 

 are, briefly, as follows : * 



1. "Malaria affects, by preference, low and moist localities" in 

 fact, swamps, fens, jungles, marshes, etc. This statement no one will 

 dispute. Conformably with it we find the mosquito does the same. 

 The female lays her eggs, to the number of two hundred and fifty or 

 three hundred, in a boat-shaped mass, on the surface of any natural or 

 artificial receptacle for fresh water. Early in spring the larvae are found 

 in the bottoms of pools and ditches, feeding upon decaying matter 

 (hence the works on entomology state that they are of great benefit in 

 clearing swamps of miasms (?)). These larva? are the so-called " wrig- 

 glers," or " wigglers," to be found in great numbers in any stagnant 

 pools of water during summer. They change into pupa?, and, in a few 

 days more, the pupa-skin is cast, and floating on this latter, like a raft, 

 the insect finally takes flight, a full-developed gnat. Many thousands 

 perish by drowning, or are devoured by fish while extricating them- 

 selves from their pupa-cases. As the eggs develop into perfect in- 

 sects in three or four weeks, many broods are hatched during the 

 warm season, which accounts for their increasing numbers during the 

 later summer and autumnal months. Some species deposit their eggs 

 in soft mud or in dry sand, but all require moisture in the larval state. 



2. " Malaria is hardly ever developed at a lower temperature than 

 60 Fahr." A temperature of G0 F. is necessary for the development 

 of the mosquito. 



3. " Tbe evolution or active agency of malaria is checked by a 

 temperature of 32 F." The mosquito is killed or paralyzed, so that 

 its active agency is checked, by a temperature of 32. 



4. Malaria "is most abundant and most virulent as we approach 

 the equator and the sea-coast." The swarms of mosquitoes (as well as 

 of sand-flies, ants, and other insect-plagues) that infest many equa- 

 torial regions are well known ; and, with regard to sea-coasts, the accu- 

 mulation of mosquitoes is both a fact and easily susceptible of expla- 

 nation. Under the influence of gentle land-breezes the mosquito is 

 wafted toward the ocean, but, in the absence of strong winds that 



* Most of them are quoted from a paper read by Dr. John T. Metcalfe, United States 

 Sanitary Commission, 1862 ; see, also, Flint's " Practice," p. 826, edition of 1867. 



