Lung Cancer Among White South Africans

to the conception, and stage C because the extent of neonatal jaundice is modified by external factors like exchange transfusion. Since the development of the human mind is a continuous process to which all three stages make their contribution, it is evident that in the final analysis each will modify the outcome in any given case of mental defect. We can merely express an opinion on which of these stages in the history of the individual is of decisive importance in order to focus attention on that stage when seeking preventive measures. Summary Aetiological problems are considered in high-grade (feebleminded and educationally subnormal) and low-grade (idiot and imbecile) mental defectives. Psychological, educational, and social factors are generally of greater aetiological significance in the former group and gross brain pathology more often operative in the latter. However, such brain pathology, in " diluted " form, also produces minor degrees of mental defect, while environmental influences have a bearing on severe defect. This is illustrated with reference to phenylketonuria, kernicterus, tuberous sclerosis, and the Sturge-Weber syndrome.