Section 9A. A student of medicine who has creditably completed not less than two years of study in a legally chartered medical school wherever located may practice medicine, but only under the supervision of an instructor in a legally chartered medical school, which instructor shall be a registered physician in the commonwealth and a duly appointed staff physician in the duly licensed hospital of not less than twenty-five beds, or an associated clinic, to which the student may be assigned. The board may, in its discretion from time to time, designate other facilities or locations in which said student may practice medicine under the conditions described above. Said students of medicine shall not sign certificates of births or deaths, nor prescribe or dispense narcotic drugs as defined in section one of chapter ninety-four C.