A practitioner of medicine; a person duly authorized or licensed to treat diseases; one lawfully engaged in the practice of medicine, without reference to any particular school. State v. Beck, 21 R. I. 288, 43 Atl. 306, 45 L. R. A. 209; Raynor v. State, 62 Wis. 289, 22 N. W. 430; Nelson v. State Board of Health , 108 Ky. 769, 57 S. W. 501, 50 L. R. A. 383.