Every time I have used comfrey to heal a wound or broken bone, I have been amazed at how well it works! The leaf has more of the allantoin than the root. To use the leaves for a poultice, you must prepare them by mixing them in a blender with a little water. Add just enough water to blend the leaves. If it is "drippy" when you take it out, you can add flour to thicken it. This is the poultice. Apply to your injury and cover.
You should not apply comfrey to a wound that is deep. This is because the would will heal from the outside in. This does not allow for drainage which may cause or increase an infection. You could trap the infection under the skin and do more harm than good.
I love teaching people about the natural medicine present in every day plants. Once my children are grown, I may consider giving workshops to teach young mothers how to care for their families naturally. I am passing it down to my sons and daughters as we go. I teach them to absorb all of the learning they can along the way because they never know what they might need later.