VRIES, G. de. C. Vlas, Hulpbetoon en afwering. Het Friese Groene Kruis 1901-1980. BMGN - Low Countries Historical Review, [S. l.], v. 118, n. 2, p. 264–266, 2003. DOI: 10.18352/bmgn-lchr.5865. Disponível em: https://bmgn-lchr.nl/article/view/URN%3ANBN%3ANL%3AUI%3A10-1-106733. Acesso em: 27 nov. 2022.