Couple of nice online summaries of Purity and Danger, Dame Mary Douglas' classic and influential 1966 book on social concepts of pollution and taboo. Douglas is a recently deceased British social anthropologist drawing particularly on Durkheim here in seeing divisions and division-making as fundamental to social order, in this case, the clean and unclean, purity and dirt.
John Durham has a great detailed overview and chapter-by-chapter summary at his website Understanding the Sacred
Victoria Caplan's summary is more a bullet-point-style report.
Excerpts from the actual book are at Google Books.