Section 73. Sections sixty-six to seventy-two A, inclusive, shall not apply to physicians and surgeons lawfully entitled to practice medicine in the commonwealth, or to persons who neither practice nor profess to practice optometry, but who sell spectacles, eyeglasses or lenses, either on prescription from such physicians or surgeons, or from optometrists authorized to practice in the commonwealth, or as merchandise from permanently located and established places of business when not sold for the purpose of correcting defective vision; nor shall said sections prevent the widow or widower of a registered optometrist, or the wife or husband of a registered optometrist who is incapacitated, from continuing the practice of optometry under a registered optometrist. Nothing herein contained shall prevent any such physician or surgeon from taking an examination and receiving a certificate of registration under section sixty-eight, nor shall this section and sections sixty-six to seventy-two A, inclusive, authorize any person to administer drugs in any form, to practice or claim to practice medicine or surgery in any sense, or to use any title or appellation intended or calculated to indicate the practice of medicine or surgery.