PHP and jquery restrict direct access

Is it possible to restrict direct access to PHP file if I use jquery .load function like this one:

$(document).ready(function(){
$("#second").load("testip.php");
});

In this case I want to restrict direct access to file testip.php that will instert data in database.

Can I do it using some PHP function that will compare visitors IP address and server IP at "testip.php" file or there is some better way to do it?

This could be helpful.

Detecting ajax events on the server

No, you can't. Unfortunately, there are no "indirect" requests in the HTTP protocol. They are all direct. From the client to the server. You can check the header below, but it can be easily faked.
And visitors IP address and server IP at "testip.php" would be always different.