jQuery(document).ready( function($) {

    $("#md_login_form").submit( function() {
        var member_login = $('#md_login_form input#md_user_login').val();
        var member_pass = $('#md_login_form input#md_user_pass').val();
        var md_login_nonce = login_register_vars.md_login_nonce;
        var data = {
            action: 'login_member',
            login_nonce: md_login_nonce,
            username: member_login,
            password: member_pass
        };
        $.post(login_register_vars.ajaxurl, data, function(response) {
            alert(response);
        });
        return false;
    });

});