The fever may precede the backache or it may follow. It may be at first a rise of only a degree or two, or it may jump to 104° F., or as high as 106° F. The latter is most frequently seen in neurasthenic subjects and in children. The pulse rises in frequency and in tension. In children a convulsion not infrequently ushers in the disease. At this time convulsions are of little significance, but late in the disease they are of serious import. There are other constitutional symptoms, such as loss of appetite, vomiting, muscular pains, a dry, coated tongue, and at times an active delirium. The face is congested and swollen. The eyes are injected and present a bleared appearance, but the watery or weeping condition seen in measles is usually absent. The nose is dry, and a sore throat is not uncommon. Epistaxis is frequent. A very important symptom which sometimes occurs in this stage is a cutaneous efflorescence, which may resemble urticaria, scarlet fever, or measles. This latter resemblance is very close and often leads to diagnostic error. The efflorescence occurs most frequently in the young, and also in vaccinated adults. In some epidemics it is not at all uncommon, but as a rule it is rare. The duration of the stage of invasion varies from two to four days. Usually it is about three days. *Period of Eruption.*--Late on the third day or early on the fourth the eruption makes its appearance, and the constitutional symptoms subside to a certain extent. The rash appears first on the confined and moist portions of the skin or in irritated parts,--under a blister, for instance, which may have been applied for the backache. Normally, it is first seen upon the forehead at the hair-line, then behind the ears and down the tender part of the neck. It gradually extends down the trunk and arms, the hands and lower extremities being affected last. The eruption generally takes from twenty-four to thirty-six hours to cover the entire body. The best location to observe the rash for diagnostic purposes is on the back, where it cannot be obscured by scratching and where the warmth of the body causes the mildest congestion to appear at its best. The exposed parts are usually ill adapted for study of the rash, being obscured by the swelling and congestion of the face and by more or less dirt or staining of the hands.