The Book of Dow has a 10-page section which provides some explanation of how and why the book was written, some of the problems encountered in gathering the data of the book and why it was printed without source information for each entry. I have recently transcribed that material. I would be happy to send it to anyone interested in having it. I can supply it as an email attachment. Just email me directly and request it. It is in Rich Text Format (rtf) and is about 36KB.