Under anatomical considerations the great number and wide distribution of very small fibers is stressed. An interesting feature is the frequent shift of individual fibers from one bundle to another, an arrangement which avoids spread of impulses to adjacent axons. The section on electrophysiological characteristics is noteworthy for an interesting discussion of the mechanism of after potentials. The most significant section of the review deals with sensory functions. By the use of an ingenious "antidromic occlusion" technique, participation of C fibers in the response to many types of skin stimulation has been demonstrated. The review concludes with mention of Bishop''s theory that C fibers form a phylogenetically older sensory system which has been supplemented by a fast conducting system of large fibers.