在codeigniter中使用自定义库中的自定义库？

the problem I am having is that I am trying to use a custom library inside of another custom library I made within codeigniter. They are both in the libraries folder and CodeIgniter tells me that I have to first load the instance of CI which I did...

class MyClass {

public function __construct()
{
    $CI =& get_instance();
    $CI->load->library("OtherClass");
}

Now inside of a function within this class I am trying to use my other library..

public function my_function()
{
      $CI->otherclass->function_inside_this_class();
}

The error I am getting is

A PHP Error was encountered
Severity: Notice
Message: Undefined variable: CI
Filename: libraries/MyClass.php
Line Number: 20

Is there something I am missing in terms of declaring the codeigniter instance itself?

Thank you!

Your CI variable scope is limited to the constructor function at the moment. You can make a class variable that has class scope and will be accessible via $this->variable in all functions within that class.

class MyClass {

private $_CI; // make a private class variable here. 

public function __construct()
{
    $this->_CI =& get_instance();
    $this->_CI->load->library("OtherClass");
}
public function my_function()
{
    $this->_CI->otherclass->function_inside_this_class();
}

I think you shouldn't use CI. Include the second_library.php and create a new class in first_library.php. Or isn't possible?