Codeigniter issues when loading Model
<?php

    class Login extends CI_Controller {

        function Login(){
            $this->load->model('membership_model');
        }

        public function index(){
            $this->load->view('login_view.php');
        }

        public function authenticate(){
            $user = $this->input->post('username');
            $pass = sha1($this->input->post('password'));
            if($user != null && $pass != null){
                $access = $this->membership_model->request_access($user, $pass);
                if($access == true){
                    $cookie = array(
                        'name'   => 'username',
                        'value'  => $user,
                        'expire' => '86500',
                        'domain' => 'unleashourmedia.com',
                        'path'   => '/',
                        'prefix' => '',
                        'secure' => TRUE
                    );

                    $this->input->set_cookie($cookie);
                    echo "cookie";
                } else {
                    redirect('login');
                }
            }
        }

    }

?>

parent::__construct();

function Login(){
  $this->load->model("membership_model","",TRUE);
  }