if (document.images) {
  image11on = new Image();
  image11on.src = "images/bmnu1-on.gif";

  image21on = new Image();
  image21on.src = "images/bmnu2-on.gif";

  image31on = new Image();
  image31on.src = "images/bmnu3-on.gif";

  image41on = new Image();
  image41on.src = "images/btn-clinical-on.gif";


  image11off = new Image();
  image11off.src = "images/bmnu1-off.gif";

  image21off = new Image();
  image21off.src = "images/bmnu2-off.gif";

  image31off = new Image();
  image31off.src = "images/bmnu3-off.gif";

  image41off = new Image();
  image41off.src = "images/btn-clinical-off.gif";

}

function changeImages() {
  if (document.images) {
    for (var i=0; i<changeImages.arguments.length; i+=2) {
      document[changeImages.arguments[i]].src = eval(changeImages.arguments[i+1] + ".src");
    }
  }
}