Incubation.--This varies from thirteen to fifteen days. In calculating this period we include the time from exposure to the appearance of the eruption. One attack generally protects the person from another attack. The period of the greatest danger of taking it extends through the period of the eruption. It diminishes as the eruption fades. From this we learn that the infection in measles takes place generally in the incubation stage. Symptoms and Description of Ordinary Type.--The first symptoms may be only a headache or a slight disturbance of the stomach. There may be some fever in the evening. There is now a redness and watery condition of the eyes, and general feeling of weariness. The cold symptoms (coryza) are not yet marked, but if we look in the mouth we may see a few spots on the mucous membrane of the cheek. Then follow the sneezing, running at the nose, sore and red eyes; running water, sensitiveness to the light, cough and fever. The eruption now appears, and is first noticed on the side of the head and the wings of the nose, as a red spotted eruption, which soon looks like a pimple, and then "blotchy." Older people feel quite sick. The aching all over, and headache are sometimes almost unbearable, especially when there is much coughing. The face, eyes and scalp are soon covered by the red rose irregularly shaped pimples, which next appear rapidly on the back of the hands, fore-arms, front of the trunk, on the back and lower extremities. This order is not always maintained. Sometimes it first appears on the back.