function suona() {
  Sound.enable();
  Sound.play($('playMusic').href, { replace: true });
  $('playMusic').innerHTML = "<b>Off</b>";
}

function playMusic(e) { 
  e.stop(); 
  if ( $('playMusic').innerHTML == "<b>Off</b>" ) {
    Sound.play('',  { replace: true });
    $('playMusic').innerHTML = '<b>On</b>';
  } else {
    Sound.play($('playMusic').href, { replace: true });
    $('playMusic').innerHTML = '<b>Off</b>';
  }
} 

document.observe('dom:loaded', function() { 
  $('playMusic').observe('click', playMusic); 
});