From Dr. David Perlmutter

"Right now, your body is colonized by a multitude of organisms that outnumber your own cells by a factor of about ten… These roughly hundred trillion invisible creatures – microbes – cover your insides and outsides, thriving in your mouth, nose, ears, intestines, genitalia, and on every inch of your skin.” 

- Brain Maker: The Power of Gut Microbes to Heal and Protect Your Brain, by Dr. David Perlmutter