The ageing of many populations in recent years has directed increasing attention to the social, medical and biological problems of senescence. The psychological changes associated with ageing occupy a central position in inquiries in this field. The expectation of mental disorder shows a steep increase with advancing chronological age, and beyond 75 years a large part of this increase is accounted for by disorders associated with degenerative changes in the central nervous system for which we lack remedies at the present time. Larsson et al. (1963) have estimated that the aggregate morbidity risk for these disorders up to the age of 70 is 0·4 per cent., up to age 75, 1·2 per cent. and up to age 80, 5 per cent. For higher ages estimates were probably less reliable, but the calculated risk up to the age of 90 was 5·2 per cent. In a survey of a random sample of elderly people aged 65 and over in the general population, Kay et al. (1964), found a total of 4·2 per cent. of elderly subjects to be suffering from senile dementia, 2·9 per cent. being mild cases. The condition is generally recognized as being a major cause of serious infirmity among the elderly in psychiatric, geriatric, general medical and community practice alike.

The brains from 50 cases of proven dementia in old age were examined and various features objectively assessed, and compared with similar features in a group of non-demented (controls) old people. Statistically significant differences were found in the two groups in relation to cortical atrophy, ventricular dilatation, senile plaque formation, Alzheimer's neurofibrillary change, granulo-vacuolar degeneration and the quantity of cerebral softening.