defaultStep = 2;
step = defaultStep;

function scrollDivDown() { 
    clearTimeout(timerDown);
    document.getElementById("content_middle").scrollTop += step;
    timerDown = setTimeout("scrollDivDown('content_middle')", 10);
}  

function scrollDivUp() { 
    clearTimeout(timerUp);
    document.getElementById("content_middle").scrollTop -= step;
    timerUp = setTimeout("scrollDivUp('content_middle')", 10);
}  

timerDown = "";
timerUp = "";

function stopMe() {
    clearTimeout(timerDown);
    clearTimeout(timerUp);
} 

document.onmousemove = function() { stopMe(); }