if (document.images) {
  btn_about_paul = new Image();
  btn_about_paul.src = root + "img/design/btn_about_paul.jpg";
  btn_about_paul_on = new Image();
  btn_about_paul_on.src = root + "img/design/btn_about_paul_on.jpg";

  btn_what_is_rolfing = new Image();
  btn_what_is_rolfing.src = root + "img/design/btn_what_is_rolfing.jpg";
  btn_what_is_rolfing_on = new Image();
  btn_what_is_rolfing_on.src = root + "img/design/btn_what_is_rolfing_on.jpg";
    
  btn_my_work = new Image();
  btn_my_work.src = root + "img/design/btn_my_work.jpg";
  btn_my_work_on = new Image();
  btn_my_work_on.src = root + "img/design/btn_my_work_on.jpg";
  
  btn_articles = new Image();
  btn_articles.src = root + "img/design/btn_articles.jpg";
  btn_articles_on = new Image();
  btn_articles_on.src = root + "img/design/btn_articles_on.jpg";
    
  btn_success_stories = new Image();
  btn_success_stories.src = root + "img/design/btn_success_stories.jpg";
  btn_success_stories_on = new Image();
  btn_success_stories_on.src = root + "img/design/btn_success_stories_on.jpg";
}

function switchOn(imgName) {
    if (document.images) {
      document[imgName].src = eval(imgName + "_on.src");
    }
}
  
function switchOff(imgName) {
    if (document.images) {
      document[imgName].src = eval(imgName + ".src");
    }
}