class Page
{
var $num;
var $text;
var $sentences;

var $i;
var $perpage;

function Page($text, $pagenum=1, $perpage=40)
{
$this->num = $pagenum;
$this->perpage = $perpage;
$this->text = $text;

$this->start = $this->perpage * ($this->num - 1); // 40*(1-1)=0, 40*(2-1)=40. This is the starting point
$this->stop = $this->perpage * $this->num; // 40*1=40, 40*2=80, this is the ending point

$this->sentences();
}

function sentences()
{
$this->sentences = explode('. ', $this->text); // Use ". " instead of just "." to avoid issues with elipses.
$this->sentences = array_filter($this->sentences, array($this, 'filter'));
}

function filter($in)
{
if ($this->i >= $this->start && $this->i < $this->stop)
{
$r = true; // Leave it in the array.
}
else
{
$r = false;
}
$this->i++; // Increment for next time.
return $r;
}

function output()
{
echo implode('. ', $this->sentences).'.';
}
}

$str = 'Hello. World. I. Am. Testing.';

$p = new Page($str, 1, 2);
$p->output();
echo '<br/><br/>';

$p = new Page($str, 2, 2);
$p->output();
echo '<br/><br/>';

$p = new Page($str, 3, 2);
$p->output();
echo '<br/><br/>';