=Development.=--Usually a week or two elapses after the entrance of the malarial parasite into the blood before symptoms occur; rarely this period is as short as twenty-four hours, and occasionally may extend to several months. It often happens that the parasite remains quiescent in the system without being completely exterminated after recovery from an attack, only to grow and occasion a fresh attack, a month or two after the first, unless treatment has been thoroughly prosecuted for a sufficient time. =Symptoms.=--Certain symptoms give warning of an attack, as headache, lassitude, yawning, restlessness, discomfort in the region of the stomach, and nausea or vomiting. The attack begins with a chilliness or creeping feeling, and there may be so severe a chill that the patient is violently shaken from head to foot and the teeth chatter. Chills are not generally seen in children under six, but an attack begins with uneasiness, the face is pinched, the eyes sunken, the lips and tips of the fingers and toes are blue, and there is dullness and often nausea and vomiting. Then, instead of a chill, the eyelids and limbs begin to twitch, and the child goes into a convulsion. While the surface of the skin is cold and blue during a chill, yet the temperature, taken with the thermometer in the mouth or bowel, reaches 102 deg., 105 deg., or 106 deg. F., often. The chill lasts from a few minutes to an hour, and as it passes away the face becomes flushed and the skin hot. There is often a throbbing headache, thirst, and sometimes mild delirium. The temperature at this time, when the patient feels intensely feverish, is very little higher than during the chill. The fever lasts during three or four hours, in most cases, and gradually declines, as well as the headache and general distressing symptoms with the onset of sweating, to disappear in an hour or two, when the patient often sinks into a refreshing sleep. Such attacks more commonly occur every day, every other day, or after intermissions of two days. Rarely do attacks come on with intervals of four, five, six, or more days. The attacks are apt to recur at the same time of day as in the first attack. In severe cases the intervals may grow shorter, in mild cases, longer. In the interval between the attacks the patient usually feels well unless the disease is of exceptional severity. There is also entire freedom from fever in the intervals except in the grave types common to hot climates. Frequently the chill is absent, and after a preliminary stage of dullness there is fever followed by sweating. This variety is known as "dumb ague."