Varicella is a benign, acute, contagious disease which occurs almost exclusively in childhood. After an incubation period of 10-14 days a rash appears, usually without premonitory symptoms, though in exceptional cases there may be fever, pains in the back and legs, malaise and even vomiting. The rash appears without particular sequence on various parts of the body, most profusely as a rule on the clothed surfaces, especially the trunk. The earliest lesions are small red macules, upon each of which there arises almost immediately a minute vesicle. The latter enlarges rapidly to about the size of a split pea.