Tuttle (philosophy, U. of New Mexico) defines the mass as any multitude which is seen dominantly as number, quantity, or externality, as opposed to individual quality or internality. He argues that the mass is the most characteristic sociohistorical feature of our century and explores work on the subject by the four thinkers named in the title. The study is well-referenced, but no index is provided. Annotation c. by Book News, Inc., Portland, Or.