The German Shepherd in Word and Picture
Fantastic resource, and definitely gives insight on the "old school" thought process...and as with many subjects, "What is old, is what is new" when it comes to analyzing where much of the breed, other working breeds, and working dog beliefs in general are derived from.
Use caution, however: when searching for a copy online, I saw a few counterfeits/cheap reprints. I was eventually able to locate an original 1920's copy in great condition. I found that often, early editions are written in a lot with notes, and hand numbered chapters, since some were issued without chapters numbered.
There are some minor translation issues, but frankly, I think it lends a unique authenticity which enhances my personal enjoyment of the text, for what it's worth.