function markThreadAsRead(fragment_url, element_id) {
  var element = document.getElementById(element_id);
  if (element != "") { 
    xmlhttp.open("GET", fragment_url);
    xmlhttp.onreadystatechange = function() {
      if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
        element.innerHTML = xmlhttp.responseText;
      }
    }
  }
  xmlhttp.send(null);
}