$(document).ready(function(){

            $.get(
                "/admin/ajax_city/", {'id': $('#id_country').val()}, function(j){
                $('#id_city').html(j);
                //$('#id_city option :first').attr("selected", "selected");
            });

            $('#id_country').change(function(){
                $.get(
                        "/admin/ajax_city/", {'id': $(this).val()}, function(j){

                           $('#id_city').html(j);
                           $('#id_city').attr('disabled', false);

                        });

            });
        });