Three weeks after college, I flew to Senegal, West Africa, to run a community center in a rural town. Life was placid, with no danger, except to your health. That danger was considerable, because it was, in the words of the Peace Corps doctor, "a fecalized environment." In plain English: s--- is everywhere. People defecate on the open ground, and the feces is blown with the dust – onto you, your clothes, your food, the water. He warned us the first day of training: do not even touch water. Human feces carries parasites that bore through your skin and cause...