$files = array('1.html', '2.html', '3.html', '4.html');

set_time_limit(0);

header('Content-Type: multipart/x-mixed-replace;boundary=myboundary');

echo "--myboundary\n";

foreach ($files as $file)
{
    $data = file_get_contents($file);
    echo "Content-Type: text/html\n\n";
    echo $data;
    echo "\n--myboundary\n";
    sleep(5);
}

echo "\n--myboundary--\n";