Section 21. An officer or person who, being employed in the state prison, suffers a convict under sentence of solitary imprisonment to be at large or out of the cell assigned to him, or suffers any convict confined in the prison to be at large out of the prison, or to be visited, conversed with or in any way relieved or comforted, contrary to the regulations of the prison, shall be punished by a fine of not more than five hundred dollars.