Brown coating on tongue

[Guest guest]

My tongue has started to be coated with very dark brown in the middle

portion of the back of my tongue. The rest of the tongue is coated with

the usual white fur - like coating.

 

I have tried using a tongue scraper but the brown remains. The tongue

scraper DOES scrape of the white though.

 

I would like some resources to learn more about this brown coating and what

to do about.

 

What web sites, books etc.... do people recommend.

 

Thank you.