$(document).ready(function(){
    
    $(".chng").click(function () {
    	var p = $(this).attr("href").substring(1);
      $("div#mo"+p).toggle();
      if ($(".modul"+p).css("background-image") == "url(http://www.tmi-medical.de/img/plus.gif)") {
      	$(".modul"+p).css({"background-image" : "url(http://www.tmi-medical.de/img/minus.gif)"});
      } else {
      	$(".modul"+p).css({"background-image" : "url(http://www.tmi-medical.de/img/plus.gif)"});
      } 
    });

});