Humphrey, E., & Warner, L. H. (1934). Working dogs: An attempt to produce a strain of German shepherds which combines working ability and beauty of conformation, by Elliott Humphrey and Lubien Warner ; with a foreword by Raymond Pearl. Baltimore: Johns Hopkins Press.

Humphrey, Elliott., and Lucien Hynes Warner. Working Dogs: An Attempt to Produce a Strain of German Shepherds Which Combines Working Ability and Beauty of Conformation, By Elliott Humphrey and Lubien Warner ; With a Foreword By Raymond Pearl. Baltimore: Johns Hopkins Press, 1934.

Humphrey, Elliott., and Lucien Hynes Warner. Working Dogs: An Attempt to Produce a Strain of German Shepherds Which Combines Working Ability and Beauty of Conformation, By Elliott Humphrey and Lubien Warner ; With a Foreword By Raymond Pearl. Baltimore: Johns Hopkins Press, 1934.