Causes.—­It occurs most frequently in low lands, along sea coasts, and swamps, particularly in the tropics and warmer portion of the temperate zone.  The exciting cause it what is called the plasmodous malarial, a parasite developing in the body of all species of anopheles, a common form of mosquito and transmitted to man, its intermediate host, by the bite of the infected mosquitoes.

Intermittent malarial fever. (a) Tertian. (b) Quartan. (c) Quotidian.  Symptoms.—­The symptoms of all these are the same, except that in tertian fever, the paroxysms occur every third day; in quartan they occur every fourth day.  Quotidian occurs daily.

The incubation time is unknown.  It consists usually of three stages, cold, hot, and sweating, and they usually occur in the morning.  “The cold stage is ushered in by yawning, lassitude and headache, and rapid rise of temperature; sometimes nausea and vomiting followed by shivering and rather violent shaking with chattering of the teeth.”  It may last from ten minutes to two hours.  The internal temperature may rise to 104 to 106 degrees, while the surface is blue and cold, with severe headache, often nausea and vomiting.  Hot stage:  this may last from one-half to five hours; the temperature may increase somewhat, the face is flushed, the skin is red and hot, great thirst, throbbing headache and full bounding pulse.  Sweating stage lasts two to four hours, and entire body may be covered; fever and other symptoms abate and sleep usually follows.  The patient feels nearly well between attacks.

Remittent or continuous malarial fever (Aestivo-Autumnal Fever).—­This form occurs in the temperate zone regions, especially in the summer and autumn.  The symptoms vary greatly.  The fever may be irregularly intermittent, but at longer intervals than the Tertian variety.  The cold stage is often absent, and in the hot the temperature falls gradually.  The appearance is often like typhoid for there may be then hardly any remission of fever.

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Pernicious malarial fever.—­This is a very dangerous disease.  The chief forms are the comatose, algid and hemorrhagic.

(a) Comatose form is characterized by delirium or sudden coma (deep sleep) with light temperature.

(b) The algid or asthenic form begins with vomiting and great prostration.  The temperature is normal or below normal.  There may be diarrhea and suppression of the urine.

(c) The hemorrhagic form includes malarial hemoglobinuria, hemoglobin in the urine.  Haemoglobin is the coloring matter of the red corpuscles.

Treatment.  Prevention.—­Destroy mosquitoes and protect from them by screens.  Small preventive doses of quinine for persons in malarious regions, three grains three times a day.  Five grains three times a day will nearly always cure tertian and quartan cases, especially if the patient is kept in bed until the time for one or two paroxysms has passed.  Attacks often stop spontaneously for a time when the patient is kept in bed, even without the administration of quinine.