function slideshow() {

    var $alt = $('#bilderstapel p.obersteebene');

    if ($alt != null) {

        if ($alt.next().length)
            var $neu = $alt.next();
        else
            var $neu = $('#bilderstapel p:first');

        $alt.addClass('mittlereebene');
        $alt.removeClass('obersteebene');
        $neu.css({ opacity: 0.0 });
        $neu.addClass('obersteebene');

        $neu.animate({ opacity: 1.0 }, 2000, function() {
            $alt.removeClass('mittlereebene');
        });
    }
}