var activ;
  // image preloader
  var img_start_Def = new Image(); img_start_Def.src = 'img/nav_start.gif';
  var img_start_MouseOver = new Image(); img_start_MouseOver.src = 'img/nav_start_over.gif';
  var img_institute_Def = new Image(); img_institute_Def.src = 'img/nav_institute.gif';
  var img_institute_MouseOver = new Image(); img_institute_MouseOver.src = 'img/institute_over.gif';
  var img_struktur_Def = new Image(); img_struktur_Def.src = 'img/nav_struktur.gif';
  var img_struktur_MouseOver = new Image(); img_struktur_MouseOver.src = 'img/nav_struktur_over.gif';
  var img_geschichte_Def = new Image(); img_geschichte_Def.src = 'img/nav_geschichte.gif';
  var img_geschichte_MouseOver = new Image(); img_geschichte_Def.src = 'img/nav_geschichte_over.gif';
  var img_infos_Def = new Image(); img_infos_Def.src = 'img/nav_infos.gif';
  var img_infos_MouseOver = new Image(); img_infos_MouseOver.src = 'img/nav_infos_over.gif';
  var img_journal_Def = new Image(); img_journal_Def.src = 'img/nav_journal.gif';
  var img_journal_MouseOver = new Image(); img_journal_MouseOver.src = 'img/nav_journal_over.gif';
  var img_tipps_Def = new Image(); img_tipps_Def.src = 'img/nav_tipps.gif';
  var img_tipps_MouseOver = new Image(); img_tipps_MouseOver.src = 'img/nav_tipps_over.gif';
  var img_fachspez_Def = new Image(); img_fachspez_Def.src = 'img/nav_fachspez.gif';
  var img_fachspez_MouseOver = new Image(); img_fachspez_Def.src = 'img/nav_fachspez_over.gif';
  var img_mitglied_Def = new Image(); img_mitglied_Def.src = 'img/nav_mitglied.gif';
  var img_mitglied_MouseOver = new Image(); img_mitglied_Def.src = 'img/nav_mitglied_over.gif';
 
  // function setActiv(imgName, imgSrc) {
   // reset imagestatus
   // document.images['start'].src = "img/nav_start.gif";
   // document.images['institute'].src = "img/nav_institute.gif";
   // document.images['struktur'].src = "img/nav_struktur.gif";
   // document.images['geschichte'].src = "img/nav_geschichte.gif";
   // document.images['infos'].src = "img/nav_infos.gif";
   // document.images['journal'].src = "img/nav_journal.gif";
   // document.images['tipps'].src = "img/nav_tipps.gif";
   // document.images['fachspez'].src = "img/nav_fachspez.gif";
   // set image activ
   // activ = imgName;
   // document.images[imgName].src = imgSrc;
  //}

  function changeImage(imgName, imgSrc) {
   // change image if not active
    if(imgName != activ) {
      document.images[imgName].src = imgSrc;
    }
  }