about those lactobacilus / acidophilus .. isn't their waste product lactic acid?? OK, so these acids (when strong enough) then kill off most other weed bacteria. And just to add in a crazy theory: what if our body shunts the lactic acid produced by hard exercise to the gut to stabilise the fermentation going on.. If this was the case then the lack of hard exercise in modern society would explain a lot about the huge increases in immune disorders that are occurring in "first world" nations (eg. asthma)
