The laws of vitality

the laws of vitality are the central points of the science of medicine, and … it is only through observations on collective vitality that any precise or numerical knowledge can be obtained representing the laws of individual vitality. The only sure index of the practical success of the science of medicine is in the increase of collective vitality, or in the diminution of collective mortality, without reference to particular diseases. Like many of his statistician and actuary colleagues – especially Benjamin Gompertz and T.R. Edmonds – William Farr believed not only that certain ‘laws of vitality’ existed, but that they could be described precisely. What Farr called ‘laws’ we would now refer to as persistent and general regularities in the structure of mortality. For example, what has come to be known as ‘Farr's law’ is concerned with the relationship between death rates and population density, while Gompertz and Edmonds are associated with the link between mortality and age, and to some extent sickness and age. Both Gompertz's ‘one uniform law of mortality from birth to extreme old age’ and Farr's law provide useful pegs on which to hang a general discussion of the structure and variations in mortality in Victorian England and Wales, especially in terms of the ways they were influenced by age and environment. This will also require us to take some account of other rather less law-like regularities in mortality patterns, such as the role of gender. The question of occupational and social variations in mortality will be left to chapter 6 and the ‘laws of disease’ will reappear in chapter 8.