r_arr = new Image();
    r_arr.src = "images/buttons/r_arr_on.jpg";
  
    l_arr = new Image();
    l_arr.src = "images/buttons/l_arr_on.jpg";

    r_arr2 = new Image();
    r_arr2.src = "images/buttons/r_arr2_on.jpg";
  
    l_arr2 = new Image();
    l_arr2.src = "images/buttons/l_arr2_on.jpg";

    function aktivieren(strg)
    {
      document[strg].src = "images/buttons/" + strg + "_on.jpg";
    }

    function deaktivieren(strg)
    {
      document[strg].src = "images/buttons/" + strg + ".jpg";
    }