All hospitals shall, at all times, have on call at such hospitals at least one licensed physician or resident interne who shall have graduated from an approved medical college, or approved osteopathic college if such hospital be an osteopathic hospital. Each hospital shall post, in a conspicuous place, a roster listing in sequence of time the names of the physicians and internes on call and the telephone numbers at which they may be reached.
35 P.S.§ 435