(4) The Central Government may make regulations for the exami- nation of the physical and mental fitness of persons subject to registration under this Act and such regulations may, in particular, enable the medical and other authority-
(a) in a case where he is unable to complete the examination on one occasion, to direct the person examined to submit himself for a further examination on a specified time and place;
(b) to direct the person examined to submit himself for examination by a specialist;