if(document.images) {
pics = new Array();
pics[1] = new Image();
pics[1].src = "images/chiro_all.jpg";
pics[2] = new Image();
pics[2].src = "images/chiro_01.jpg";
pics[3] = new Image();
pics[3].src = "images/chiro_02.jpg";

}
  function changer(from,to) {
  if(document.images) {
  document.images[from].src = pics[to].src;
    }
  }