John Burdon Sanderson Haldane (1892-1964) was Professor of Genetics at UCL from 1933 to 1937 and of Biometry (Biostatistics) from 1937 to 1957. He was first invited to Sweden by the Mendelska Sällskapet, the first Swedish Genetics association founded in 1910, in 1943 but was unable to travel due to the war. He was only able to accept the invitation in March-April 1946 as he travelled to Lund in Sweden as well as Copenhagen in Denmark as part of an official visit to various institutions. The Haldane Papers at UCL include the correspondence relating to this journey and to other proposals for collaboration by Danish and Swedish colleagues and media.
In addition to the sample featured here, note that the Wellcome Library has digital copies of all these documents available as part of its online archives.
Location: UCL Special Collections, Haldane Papers