input for stateChanged()

Hi
When I want to define input variable for stateChanged, my code doesn't work
I don't want to define lots of stateChanged functions. How can I fix it?
This code doesn't work:

function loadrealms(str)
{
xmlhttp=GetXmlHttpObject();
if (xmlhttp==null)
  {
  alert ("Your browser does not support AJAX!");
  return;
  }
var url="ajaxphp.php";
url=url+"?action=loadrealms&region="+str;
xmlhttp.onreadystatechange=stateChanged('realmoptions');
xmlhttp.open("GET",url,true);
xmlhttp.send(null);
}

function stateChanged(div_id)
{
if (xmlhttp.readyState==4)
  {
  document.getElementById(div_id).innerHTML=xmlhttp.responseText;
  }
}

Code (markup):

But this code works fine:

function loadrealms(str)
{
xmlhttp=GetXmlHttpObject();
if (xmlhttp==null)
  {
  alert ("Your browser does not support AJAX!");
  return;
  }
var url="ajaxphp.php";
url=url+"?action=loadrealms&region="+str;
xmlhttp.onreadystatechange=stateChanged;
xmlhttp.open("GET",url,true);
xmlhttp.send(null);
}

function stateChanged()
{
if (xmlhttp.readyState==4)
  {
  document.getElementById("realmoptions").innerHTML=xmlhttp.responseText;
  }
} 

Code (markup):