Bowden, Mary Ellen (1997). "Svante August Arrhenius". Chemical achievers : the human face of the chemical sciences. Philadelphia, PA: Chemical Heritage Foundation. pp. 32–34. ISBN9780941901123.
Koukopoulos, A. (January 2003). "Ewald Hecker's description of cyclothymia as a cyclical mood disorder: its relevance to the modern concept of bipolar II". Journal of Affective Disorders. 73 (1–2): 199–205. doi:10.1016/S0165-0327(02)00326-9. PMID12507752.
Koukopoulos, A. (January 2003). "Ewald Hecker's description of cyclothymia as a cyclical mood disorder: its relevance to the modern concept of bipolar II". Journal of Affective Disorders. 73 (1–2): 199–205. doi:10.1016/S0165-0327(02)00326-9. PMID12507752.