In an inquest under this chapter, the coroner may issue subpoenas for witnesses returnable forthwith or at such time and place as he may appoint. He must summon and examine as a witness any person who, in his opinion or that of any of the jury, has any knowledge of the facts; and he may also summon as a witness a surgeon or physician who must inspect the body in the presence of the jury and give a professional opinion as to the cause of death.