Recurrence of Aortic Coarctation after Operation in Childhood

that this tumour may be induced by an enviromnental factor. The age distribution both in the indigenous and in the immigrant population suggests that this factor produces immunity in the majority of people exposed to it and tumour only in rare instances. The apparent dependence on temperature of the tumour distribution suggests that the environmental agent is transmitted by an insect vector and that either the distribution of the vector or the development of the agent within the vector is dependent on temperature. This agent might be an arbovirus or other insect-vectored virus; it could also be some other form of parasitic disease such as malaria.