Any supervisor who (a) refuses or neglects to perform any duty imposed on him, without just cause, or (b) wilfully violates any law provided for his government as a supervisor, or (c) fraudulently or corruptly performs any duty imposed on him, or (d) wilfully, fraudulently, or corruptly attempts to perform an act as supervisor which is unauthorized by law, in addition to any other penalty prescribed by law, forfeits to the county five hundred dollars ($500) for every such act, to be recovered on his official bond, and is further liable on his official bond to any person injured thereby for all damages sustained.