PHP/Class/self

Use self to reference static class properties

<?php
   class visitors
   {
      private static $visitors = 0;
      function __construct()
      {
         self::$visitors++;
      }
      static function getVisitors()
      {
         return self::$visitors;
      }
   }
   $visits = new visitors();
   echo visitors::getVisitors()."<br />";
   $visits2 = new visitors();
   echo visitors::getVisitors()."<br />";
?>