function imageOn(tagname) {
  var obj;
  if (document.images) {
 
       // alert ("at middle of image on." + tagname);
        //Swap the lable
    obj = eval("document." + tagname);
        obj.src = onImgArray[tagname].src;
    
  }
} 

function imageOff(tagname) {
  var obj;
  if (document.images) {

        
        //Swap the lable
        obj = eval("document." + tagname);
        obj.src = offImgArray[tagname].src;
        //alert ("at end of image off." + tagname)
  }
}