MALAR, mteliir, or MAELAR. One of the largest and most beautiful lakes in Sweden, stretching for seventy miles westward from Stockholm. with a breadth of from 2 to 23 miles (Alain Sweden, G 7). Its waters arc nearly on a level with the Baltic Sea, into which they are discharged by channels running through and around the city of Stockholm. The lake contains over 1200 islands, and the scenery along its shores is much varied with wood, lawn, and cliffs, and adorned with castles, country-seats, and villas. The surrounding country is fertile and populous, and upon the shores stand the towns of Enkiiping, Vesterils, Strengniis, and a number of villages. MALARIA (from It. vial' aria, had air, from niula, fem. sg. of mak). from Lat. males, bad, and aria, from Lat. from Gk. ecijp, air, from derv, aria, to blow), and 'MALARIAL FEvEn. This disease was until recent years regarded as a poisonous emanation (whence the name) from the soil of certain localities, but is now definitely known to lie one of the specific infectious dis eases, and to be caused by an animal parasite peculiar to the blood of man and mosquitoes—the Plasmodium malarial. This parasite, discovered in ISSO by Laveran (q.v.) belongs to a class of protozoa called hcmocytozoa or hentosporidia which attack and develop in the red blood cor puscles of animals, birds, and fish, and of which numerous species are known. In the human blood several varieties of the parasite have been dis tinguished, each associated with a definite type of fever. These are the parasites of tertian, guar tan, and :estivo-autumnal fever. It was first pointed out by Golgi that the tertian and quar tan parasites exist in the blood in great groups, all the members of which are at approximately the sanie stage of development. An entire group, for example, undergoes sporulation within a few hours' time, and this sporulation is always ac companied by the malarial paroxysm. The ter tian parasite requires about forty-eight hours to accomplish its life cycle and produce spores; the quartan about seventy-two hours; so that in a single infection with one or the other of these parasites we observe the characteristic malarial paroxysm on every third and every fourth day, respectively. Double infection, that is. the in troduction of two separate groups of parasites at different times, may occur, however, and produce daily paroxysms or attacks on two successive days. with a day's intermission. etc. The exact
duration of the life cycle of the cestivo-autumnal type of parasite is less definitely understood. Sporulation may occur at irregular intervals, or may take place continuously, and the resulting fever is correspondingly irregular and sometimes almost continuous. The plasmodium may be observed in the blood of individuals suffering from an attack of malarial fever, moving about in the plasma or attacking and destroying the red blood corpuscles. It begins its life cycle as a small round or oval hyaline ammboid body. The tertian variety is the largest, and is about the size of a red corpuscle of an inch in diameter). The wstivo-autumnal variety is less than half that size, the quartan somewhere be tween the two. The red corpuscles attacked become expanded or shrunken, and ilecolorized, and the pigment collects in clumps of granules. Later on, long, active processes called flagclhc develop from the full-grown parasite, and move about freely in the blood. These are believed to be the sexual elements.
The most brilliant chapter in the history of malaria investigation records the series of ex periments by Hose. Manson. and others which proved that the disease was not air-borne, but communicated exclusively by the bites of mos quitoes which serve as intermediary hosts for the parasite, and are the sole agents of infection. Only a particular family of mosquitoes—the anophcics—are capable of communicating the dis ease. Of these three species have been recognized in this country. The Anopheles quadrimaculatus is most concerned in the spread of malaria in the United States, and is probably identical with Anopheles cloriger, the most active agent in Europe. Until the truth of the mosquito theory was established, the only protection against malaria was quinine. Now, however, a much more effective defense is possible for those com pelled to live in malarious districts. This con sists in shielding themselves from the bites of mosquitoes, especially at night, by the use of nets and screens; in waging a constant warfare upon the insects by draining pools and marshes where they breed; and in destroying their lame by the liberal use of petroleum dur ing the malarial season. See INSECTS, PROPAGA TION OF DISEASE BY.