As is well known, chickenpox is one of the very mildest of the infectious diseases to which children are subject. It possesses, however, considerable medical interest, as one of the group of diseases of unknown origin, and furthermore, because of its remarkable communicability. In the latter particular it is rivalled only by measles. In the Home for Hebrew Infants it has been our experience that in the course of an epidemic about three quarters of the younger children develop varicella, and about one half of those above 2 years of age. It spreads rapidly through the institution, progressing from ward to ward in an uncontrollable manner, frequently necessitating quarantine for a period of many months. Among children in private homes it possesses a serious pedagogic aspect, often disrupting the school sessions for long periods because of its widespread prevalence and long incubation period, which causes the infection to drag along