The provisions of § 99.01 shall not apply to sheriffs, coroners, constables, members of the police force, or other peace officers engaged in the discharge of their official duties, or to any person summoned by any of these officers to assist in making arrests or preserving the peace, while the person so summoned is engaged in assisting the officer, or to any person engaged in the necessary defense of human life under circumstances permitted by law.
('69 Code, § 11-11)