General ⇒ \small font in \newtheorem environment

[zorzal]

In a book:
\documentclass[11pt]{book}

I defined:
\newtheorem{Ex}{Example}[chapter]

to set Examples in a font different from the rest of the book. By default, they come up in italics, I think because I am using
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}

How can I make the fonts also \small within the environment ?

Currently I have to type \small every time, as follows:
\begin{Ex}\small%
An example goes here ...
\end{Ex}%
which bothers me because I forget.

Thank you.
Zorzal

[localghost]

The answer to your request has already been given elsewhere. I would appreciate if you mention that you do a cross posting. That saves me the time I would spend to think about your request.