The attack may be sudden, but it is usually preceded by a feeling of languor, yawning, and general discomfort; this is followed by the _cold stage_, which, in the tropics, is usually short, and in the more ordinary attacks is ushered in by a violent shivering fit or rigor, though this is not common in Central Africa. The sensation of cold is entirely subjective, for though the patient feels chilly and piles clothes upon himself his temperature will be found elevated. At this period violent vomiting is not infrequent. Then comes the _hot stage_, often of long duration, followed by the _sweating stage_, during which the perspiration pours from the patient and soaks everything on and about him. After this there is a period of remission, or intermission of the feverish symptoms with corresponding relief to the patient. Usually, after some hours, the attack comes on again, beginning with the cold stage, but if the fever is treated very early, the disease may now pass off. The whole attack lasts as a rule from six to ten hours, say one hour for the cold stage, three or four for the hot period, and two to four for that of defervescence. There is sometimes a feeling of pain and discomfort in the right side owing to the congestion of the spleen, which enlarges during the rigor. There are three distinct species of malarial parasite, and each causes a different type of fever. According to the type with which the patient has become infected, the fever recurs after one, two, or three days. At the same time all kinds of febrile irregularities are met with, so that it is often impossible to diagnose the disease in the absence of blood examination for the detection of the parasite. Anæmia is a constant feature of the malarial attack, as is but natural, considering the great destruction of red blood cells brought about by the parasites which have infected them.