var current=1;

	function showIt(cell_to_show) {
		if (document.getElementById(cell_to_show)) {
				document.getElementById('cell_1').className="hide_it";
				document.getElementById('cell_2').className="hide_it";
				document.getElementById('cell_3').className="hide_it";
				document.getElementById('cell_4').className="hide_it";
				document.getElementById(cell_to_show).className="show_it";
		}
	}

	function autoNext() {
		current = current + 1;
		if (current > 4) { current = 1; }
		cellName = 'cell_' + current;
		showIt(cellName);
	}

	function startShow() { intervalID = setInterval("autoNext()",3000); }

	function pauseShow() { clearInterval(intervalID); } 

	startShow();