Where is "load" object created?

[eluser]Unknown[/eluser]
I've been digging through the CodeIgniter code to try and understand how it works on a deeper level. Starting with the index.php file and moving through the files as it appears that they are loaded into memory, but I am having trouble finding where the 'load' object is created as in: this->load->library(). I'm still learning php and it's likely that I have missed the place where this happens, so I was wondering if any CI experts out there might give me a pointer?

Thanks,
Mark