Buiting, M.H.J. “S. Bloemgarten, Henri Polak, Sociaal Democraat, 1868-1943”. BMGN - Low Countries Historical Review 110, no. 1 (January 1, 1995): 141–143. Accessed March 29, 2024. https://bmgn-lchr.nl/article/view/URN%3ANBN%3ANL%3AUI%3A10-1-104584.