Epidemiology in Country Practiceby William N. Pickles, published in 1939, has been a source of continuing interest and challenge especially to general practitioners (Watson, 1982; Booth, 1987). Pickles worked for over 50 years as a general practitioner (GP) in rural Wensleydale where there were many isolated villages in which natural immunity against various infections was often lacking. And so the source of infection could usually be traced, and, with little or no immunity, spread was often rapid.