An amazing thing about the human body is that it tends to reject anything that is foreign to it.  Take a splinter, for instance, which has worked its way under your skin as a thorn did my thumb when I was pruning my roses.  Unable to dig it out with a needle, I said to myself, "I'll just let nature take care of it," and sure enough, it was sore for a few days and then the surface around the thorn toughened as the flesh began to isolate the foreign object.  In a few days, the thorn worked to the surface where I could get it with tweezers.