Intestinal bacteria have an effect on the nervous system: they affect how we think and how we feel and how our mind develops. This is pretty recent science written by scientists about the function of our mind (or murine minds, at least). That makes it an interesting rationality quote, in my opinion.
Really? If true, then that is fascinating... Can you link to any of the recent research, though?
Here's the new thread for posting quotes, with the usual rules: