During the course of the past hundred years countries such as Britain have seen a very marked change in their patterns of morbidity and mortality. For example, between 1848 and 1872 it has been estimated that over 32 per cent of all male deaths in England and Wales were caused by infectious diseases and that only 6 per cent were the result of cancer and diseases of the circulatory system. By 1970 the respective figures were 0.6 per cent and 56.6 per cent. In 1848-72 mortality between the ages of one and four has been estimated at 36.5 per 1,000, while in 1970 it was under 1.1 per 1,000 (males). Today about 3 per cent of the total deaths experienced by the population of Britain occur in children under five whereas a century ago they accounted for over 40 per cent.