Under the provisions of title XVIII as originally enacted, an individual eligible
            for SMI had to take the positive action of filing a written request for enrollment.
            While most individuals did enroll, some persons who wanted SMI failed to enroll at
            their first opportunity because of senility, misunderstanding, or other reasons.
         
         Since the enrollment provisions are so strict, many incurred medical expenses before
            they had the opportunity to enroll again.