Letter, 27 June 1870
Letter, 4 June 1870
Letter, 15 June 1870
Letter, 30 January 1872
Letter, 30 November 1871
Letter, 22 December 1877
Letter from Sir John Burdon Sanderson, August 2, 1884
Letter, 3 August 1887
Letter, 15 April 1888
Letter to Harvey Cushing, 1890