Cause.--An unknown poison in the contents of the pustules or crusts in secretion and excretion, apparently, and in the exhalations of the lungs and skin; one attack does not always confer immunity for life. It is contagious from an early period. Direct contact does not seem to be necessary, for it can be carried by one who does not have it. Symptoms.--Incubation lasts from ten to fourteen days, and is usually without symptoms. Invasion comes suddenly with one or more chills in adults, or convulsions in children, with terrible headache, very severe pain in the back and extremities, vomiting, the temperature rising rapidly to 103 or 104 degrees. Eruptions.--This usually appears on the fourth day as small red papules on the forehead, along the line of the hair and on the wrists, spreading within twenty-four hours over the face, extremities, trunk and mucous membrane. Symptoms of fever diminish with the appearance of the rash, which is most marked on the face and ripens first there. The papules become hollowed vesicles and a clear fluid fills them on the fifth or sixth day. They fill with pus about the eighth day, and their summits become globular, while the surrounding skin is red, swollen and painful. The general bodily symptoms again return and the temperature rises for about twenty-four hours. Drying of the eruption begins the tenth or eleventh day. The pustules dry, forming crusts, while the swelling of the skin disappears and the temperature gradually falls. The crusts fall off, leaving scars only where the true skin has been destroyed. Confluent form.--All the symptoms are more severe. The eruption runs together and all the skin is covered. Varioloid.--This is smallpox modified by vaccination. The invasion may be sudden and severe. It is usually mild and gradual, but with severe pain in the back and head. A scanty eruption of papules, often only on the face and hands, appears on the third or fourth day, with disappearance of constitutional symptoms. [202 MOTHERS' REMEDIES] Treatment.--Vaccinate the children the second or third month, and all persons about every six years, and always after exposure to the disease or during epidemics. Put the patient in a room cleared of all furniture, carpets, curtains, rugs, etc.; keep the patient thoroughly clean, and the linen should be frequently changed. The bed clothing should be light. Disinfect and sterilize everything thoroughly that has been in contact with the patient. Get a good experienced nurse, and one who has been around the disease.