n. Air contaminated with some pathogenic substance from the soil; specifically, air impregnated with the poison producing intermittent and remittent fever.n. The disease produced by the air thus poisoned.n. Numerous investigations made in recent years have established the fact that malaria is a disease resulting from the presence within the red blood-corpuscles of a protozoan parasite, the Hæmamœba malariæ, or Plasmodium malariæ. The parasite has two cycles of existence, one in the human body, the other in the body of a mosquito of the genus Anopheles (which see, with cut). In the blood, reproduction of the parasite occurs only by fission or segmentation; but in the stomach-wall of the mosquito, which it reaches in the blood sucked by this insect from the skin of the sick, sexual reproduction occurs, the parasite giving birth to a large number of exceedingly minute forms, called sporozoids. These make their way through the tissues of the mosquito to its salivary glands, whence they are injected into the blood of the human subject whom this infected mosquito stings. On reaching maturity in the blood, the protozoan invades the red blood-corpuscles, and so completes the two cycles of its existence. The malarial paroxysm of chill, fever, and sweating occurs at the time of invasion of the blood-cells by a new brood of the parasites, either those resulting from segmentation of the protozoan within the human blood-vessels or those reproduced sexually in the body of the mosquito and thence injected into man. There are three varieties of the Hæmamœba which are concerned in the production of the three varieties of malaria, tertian, quartan, and estivoautumnal or pernicious. Symptomatically, there are four forms of malaria: the intermittent, in which the interval between the paroxysms is fever-free; the remittent, in which the fever is continuous, but is marked by exacerbations with intercurrent chill and sweating; the pernicious or congestive form, in which the blood-poisoning is profound; and the chronic form, constituting what is called the malarial cachexia. See Laverania.
