Section 4106. Alternate jurors

Unless the court, in its discretion, orders
  otherwise, one or two additional  jurors,  to  be  known  as  "alternate
  jurors",  may be drawn upon the request of a party. Such jurors shall be
  drawn at the same time, from the same source, in the  same  manner,  and
  have  the  same  qualifications as the regular jurors, and be subject to
  the same examinations and challenges. They shall be  seated  with,  take
  the  oath with, and be treated in the same manner as the regular jurors,
  except that  after  final  submission  of  the  case,  the  court  shall
  discharge  the  alternate jurors. If, before the final submission of the
  case, a regular juror dies, or becomes ill, or for any other  reason  is
  unable to perform his duty, the court may order him to be discharged and
  draw the name of an alternate, who shall replace the discharged juror in
  the  jury  box,  and be treated as if he had been selected as one of the
  regular jurors.