Much of the research I have undertaken has occurred as a result of serendipity, ‘the faculty of making happy and unexpected discoveries by accident’. The word was first used by Horace Walpole in 1754 and was taken from the story of the three princes of Serendip, the old name for Sri Lanka. Serendipity in medicine has been beautifully discussed by Richard Asher in his book Talking Sense.He defines it as an ability to recognise the Highest Common Factor, or HCF. McFarlane Burnett has remarked that recognition of the HCF involves what he describes as the ‘notebook and shoe leather method’ or ‘shoe leather epidemiology’.

It was by lucky chance that I went as a ship's surgeon to South Africa and found that multiple sclerosis was uncommon there and unknown among the black population. Then it was by serendipity that I should find myself in practice in Port Elizabeth in the Eastern Cape, the area in Southern Africa with the highest prevalence of porphyria.

My greatest personal interest was to further research into the causes of multiple sclerosis. As I have explained, MS had a high prevalence among immigrants from Europe, but is much less common among the white South African-born. Returning to Europe from South Africa gave me an opportunity to study what had happened to those who came from low MS prevalence areas of the world, such as Asia, Africa or the West Indies, to Britain, a high MS prevalence area. I knew that after the Second World War, over two million immigrants had come to Britain from Asia, mostly from the Indian subcontinent, from Africa, particularly Asians from East Africa and from the Caribbean. The majority had settled in Greater London and the West Midlands. I knew that MS was very uncommon among Asians, whether they were born in Asia or in East Africa, and that it was relatively uncommon in the West Indies. I decided, therefore, to study the records of all patients diagnosed as having MS who had been admitted to hospital in Greater London between 1960 and 1972. The first study was undertaken in collaboration with Dr Abraham Adelstein, director of the Office of Population Censuses and Surveys, London.