1. http://www.personalliberty.com/alternative-medicine/medicinal-benefits-of-redmond-clay/
2. http://www.umm.edu/altmed/articles/comfrey-000234.htm
3. http://en.wikipedia.org/wiki/Comfrey
4. http://www.springerlink.com/content/n31120p217335w71/
5. http://www.ncbi.nlm.nih.gov/pubmed/16510384
6. http://www.springerlink.com/content/a441721x13w36g26/
7. http://www.ncbi.nlm.nih.gov/pubmed/14518351
8. http://www.ncbi.nlm.nih.gov/pubmed/17169543