its a complicated subject to say the least....
and it quickly becomes obscure with all the
scientific mumbo jumbo...used sometimes....
i read constantly about it and found the
language (analogies) used in this article to be
much easier to understand the basics.
i'm not endorsing the product line but
thought it was useful enough to share
especially on the echinacea herb....
http://www.askdrsears.com/html/4/t042500.asp