function Md(Nr) {
var oldPic = document.images[Nr].src;
var off = oldPic.lastIndexOf("r");
if (off != -1) { /* Sicherheitsabfrage */
var newPic = oldPic.substring(0,off) + "b";
document.images[Nr].src = newPic + ".gif";}}

function Mw(Nr) {
var Bild = document.images[Nr].src;
var on = Bild.lastIndexOf("b");
if (on != -1) { /* Sicherheitsabfrage */
var newPic = Bild.substring(0,on) + "r" + Bild.substring(on + 1, Bild.length);
document.images[Nr].src = newPic;}}