// http://www.w3.org/TR/REC-CSS2/visufx.html#visibility
document.getElementById('Saisi').style.visibility='hidden';
// visibility = visible || hidden || collapse (pour TR)
// http://www.w3.org/TR/REC-CSS2/visuren.html#display-prop
document.getElementById('Saisi').style.display='none';
// display = none || '' || block || inline ...