Letters: Engels To George Julian Harney Genoa, 5 October 1849 https://marxistleninists.org/M&E/1849/letters/49_10_05.htm
Lenin: The Dying Autocracy and New Organs of Popular Rule https://www.marxists.org/archive/lenin/works/1905/nov/23.htm
Letters: Engels To Jakob Lukas-Schabelitz Lausanne, 24 August 1849 https://marxistleninists.org/M&E/1849/letters/49_08_24.htm
Economic Manuscripts: Capital Vol. I - Chapter Eleven http://hiaw.org/defcon6/works/1867-c1/ch11.html