Why is it that when bismuth is combined with salicylate, or salicylic acid, (as in Pepto-Bismol), it is a digestive system reliever? More interestingly, why does the medication turn the tongue and stool black? (It can also make the tongue "hairy.") I have looked at all the medical sites and all I can find out is [i]that[/i] it turns them black, not [i]why[/i]. I also read that salicylic acid can be used in dyes. Is that one reason?