1. Conrad J. Lord Jim: A tale, Edinburgh and London: William Blackwood and Sons, 1900, pp. 340–340.
2. Darwin's Illness
3. Burkhardt F, Smith S. The correspondence of Charles Darwin, vol. 4, Cambridge: Cambridge University Press, 1989, pp. 225–225.
4. Burkhardt F, Porter D, Dean SA, et al. The correspondence of Charles Darwin, vol. 11, Cambridge: Cambridge University Press, 1999, pp. 602–603.