Mortality statistics have now been available for the population of Great Britain for just over a hundred years and during this period there has been a steady and sustained decrease in mortality at all ages and in both sexes, though the extent of the decrease has been progressively less with increasing age.

The main part of the improvement in mortality during the latter half of the nineteenth century was due to improvements in sanitation and hygiene and above all the provision, at any rate in cities, of a reasonably safe water supply. Cholera which occurred in severe epidemic form in London between 1832 and 1866 had disappeared completely well before the beginning of the twentieth century. The widespread epidemics of typhoid fever which occurred as a result of water supplies becoming contaminated with sewage ceased when adequate precautions were taken to safeguard the sources and transmission of water in cities. It is true that small and localized epidemics of typhoid still occur, but these are all found to be due to contamination of food or water by ‘typhoid carriers’. A recent epidemic in Wales, in which some 150 cases of typhoid occurred, was shown to have been caused by the eating of ice-cream which was handled and sold by a man in perfect health but who, following an attack of typhoid many years previously, had continued to pass virulent typhoid organisms in the stools. Fortunately the notification of cases of the disease enables the public health authorities rapidly to track down carriers in this type of epidemic.