Since Degkwitz1 published his first report on the prophylactic value of convalescent serum against measles, this method of prophylaxis has been used more or less in every epidemic in Iceland. Owing to the isolation of the country, many years may elapse between two epidemics of measles. In the last century over twenty years could pass between epidemics, and when the disease at last was brought in it swept like a fire, attacking people of all ages and killing great numbers of them, behaving on the whole like a dangerous disease. In 1846 it killed 2,000 people, or 35 per thousand of the entire population. In 1882 the mortality rate was 24 per thousand of the whole population. Such enormous mortality rates are no longer seen, and the intervals between epidemics have grown shorter, now usually being about seven years. The disease, on the whole, runs a much milder course,