function changeClass(elName,cntPictures){
	var el = getE(elName);
	var entries = cntPictures;
	var klasse = "zufall"; 
	if(changeClass.arguments.length>2){
		klasse = changeClass.arguments[2];
		}
	random_number =  Math.ceil(Math.random()*entries)
	el.className+=" " + klasse + "_" + random_number;
	}