Matthew Wood talks about this basic paradigm of traditional Western herbalism. The concept of "purifying the blood" goes back to our European folk medical roots. There also seems to have been an analogous concept in American Indian medicine. Scientific doctors of the nineteenth century, while admitting that there was something to these remedies, could not explain their action. Thus they adopted the term "alterative,'' meaning that these remedies " altered the system in some unknown fashion." This is not a definition so much as a lack of one. As modern medicine emerged there was no place for "alteratives" much less "blood purifiers." This placed the modern herbalist in a difficult position. There is no scientific basis for the use of alteratives or blood purifiers and yet, many of our remedies are defined as such. For more details on this presentation go to the following URL: http://www.frontiercoop.com/Frontier/HerbFest/2000Seminar/2000Purifying.html