Heredity, environment, the role of infectious agents, and other influences have been cited within a multiplicity of factors of possible relevance to the problem of neoplasm etiology. In some cases, such as that of retinoblastoma the influence of hereditary factors has been clearly established. The influence of genetic factors in cerebral tumour development has been under discussion since as early as 1896 when Besold reported two sisters suffering from brain tumours. Although much more is now known about the classification, prognosis, and treatment of these tumours, and a number of familial...