Comfrey

The genus name for comfrey  is Symphytum, which means to "unite or knit together." The name com-firma means simply, "knitting of bones." You can use the leaf and the root, fresh or dried. Comfrey contains a special substance called allantoin, which is a cell proliferative. In other words, it makes cells grow faster. This is one of the reasons why comfrey-treated bones knit so fast, wounds mend so quickly and burns heal with such little scarring. Comfrey is often called knitbone or healing herb.  

This same substance, allantoin, is found in the placenta of a pregnant mother which helps the baby grow rapidly. After the baby is born, allantoin is also found in the mother's milk — abundantly at first and less so as the child grows.