It shall be unlawful for any person to engage in the practice of medicine, surgery, osteopathy, optometry, naturopathy, podiatry, or any other system of the treatments of injuries, diseases, pain or deformity, or to hold himself forth as a practitioner thereof or to assume the title of Doctor in relation thereto, except as provided in this subchapter. This subchapter shall not apply to dentistry, nursing or chiropractic.