var varid
function xiangxia(){
if (varid==undefined)
varid=setInterval("ck4918.scrollBy(0,-3)",20);
}
function ting()
{
clearInterval(varid);
varid=undefined
}
function xiangshang(){
if (varid==undefined)
varid=setInterval("ck4918.scrollBy(0,3)",20);
}