The geography of neurology.

Medical geography, although an ancient form of our art, cannot be said to have really fulfilled its early promise. Although striking geographical variations have been disclosed in the incidence of many diseases?for example, in the case of gastric carcinoma?we seem to be no nearer causation. In the eighteenth and nineteenth centuries there were many accounts of the afflictions encountered in particular regions or countries, and some of them contained the first major description of a disease. Hillary's published observations in Barbados1 include a vivid account of tropical sprue, Casal y Julian gave a description of pellagra in the Asturias,2 Rutty described relapsing fever in Dublin,3 and Winterbottom described sleeping sickness (African trypanosomiasis) in Sierra Leone.4 Hirsch's classic Handbook of Historical and Geographical Pathology* would probably have had more impact if the era of bacteriology had not so quickly dawned. Medical geography seemed unimportant at a time when nearly every year a new organism was identified as a cause of some human disease. Sigerist8 believed that medicogeographical studies became somewhat discredited because "previous work had in many ways been too ambitious, attempting a synthesis before the materials were available." Nevertheless, comparative studies of diseases in different ethnic, national, and social groups might be expected to help in three ways. Firstly, by identifying communities which show a major difference in the frequency of a disease of unknown causation, such as multiple sclerosis, some light may be cast on aetiology. Secondly, the value of a hypothesis about the cause of a disease may be tested by examining the incidence of the disease in communities which are exposed to the suspected