The problems of the interdependence and unity of the brain and body have been put on a scientific basis by Pavlov and his successors. Bykov (1947) has, for example, been able to demonstrate that the cortex plays a leading part in the regulation of somatic processes, such as secretion of urine, blood pressure, peristalsis and metabolism. It is therefore reasonable to argue that lesions of the central nervous system will be reflected in the pathogenesis and course of morbid processes in the body. It does not follow, however, that this influence will necessarily be in the direction of greater lability, more rapid pathogenesis or more extensive destruction. The outstanding feature of the central nervous system is its plasticity and power of compensation. It is therefore possible and probable that those parts of the nervous system which remain intact will take over and compensate for the function of the lost ones. Emotion may, for example, lead to polyuria, but it does not follow that urinary secretion will be impaired in a leucotomized patient. The brain may well play an important part in the infective processes of a normal person, but the defence against infection in a microcephalic idiot may remain perfectly adequate, and may even be more effective than in a normal person, provided that the mechanism of the immunity and phagocytosis had been more fully mobilized in the course of his previous life.