更新页面内容而不刷新页面？

Question

If I included a file like this:

<?php
include "counter.php";
?>

..and my HTML is like this..

<p><?php echo $counter ?></p>

Is it possible to reread counter.php on a regular interval? The data in that file changes constantly and I would like to display those changes without reloading the page.

EDIT: $counter is a variable within counter.php