[Theories concerning viruses and neoplasms]

The causes of neoplasia are discussed with particular reference to viruses. Stress is laid on some differences between the mainly cytolytic action of viruses in man and their possible cancerigenic power. It is felt that neoplasia arises from a variety of aetiologies, mostly of an irritative nature, coupled with a single, final pathogenetic mechanism linked to chromosome changes that do not result in the death of the cell.