Richardson, Genesee (1891). "John Plakinton". Biographical Sketches of Increase Allen Lapham: And Other Distinguished Citizens of Wisconsin ... Cramer, Aikens & Cramer. p.29. Archived from the original on 5 August 2020. Retrieved 2 March 2019.
Sponsel, Rudolf. "J.L.G. Ferris (1863–1930)" (in German). Allgemeine und Integrative Psychotherapie. Archived from the original on 13 June 2010. Retrieved 1 August 2010.
Richardson, Genesee (1891). "John Plakinton". Biographical Sketches of Increase Allen Lapham: And Other Distinguished Citizens of Wisconsin ... Cramer, Aikens & Cramer. p.29. Archived from the original on 5 August 2020. Retrieved 2 March 2019.
Sponsel, Rudolf. "J.L.G. Ferris (1863–1930)" (in German). Allgemeine und Integrative Psychotherapie. Archived from the original on 13 June 2010. Retrieved 1 August 2010.