A Comparison Through

Studies with the cathode ra.y oscillograph have shown that the fibers composing a peripheral nerve range widely in their reactivities. For instance, a large nerve, such as the sciatic, contains fibers conducting at rates varying as widely as 50 to 1 with an even wider irritability range as determined by induction shocks. But neither in this nor in other nerves is there an even numerical distribution of fibers with respect to these properties. The uneven numerical distribution of fibers with respect to conduction rate is manifested in the consistent elevations which appear on the maximal, conducted action potentials of large nerves. Attempts have been made bo trace to their sources the fibers contributing their potentials to the several elevations and to ascertain the functions the component fibers subserve (Erlanger, Bishop and Gasser, 1926; Erlanger, 1927; Erlanger and Gasser, 1930; Bishop and Heinbecker, 1930). Bishop and Heinbecker recognize four types of fibers, namely A, B1, B2 and C, present in varying combinations according to nerve and species. “The ordinary mixed somatic nerve,” they say in one of their latest publications (Heinbecker, Bishop and O’Leary, 1932), “gives rise to all four. The fibers responsible for the A component,” they go on to say, “are the large thickly myelinated ones known to include, primarily, somatic motor and sensory elements. The B1 component includes primarily the somewhat smaller and frequently somewhat more thinly myelinated fibers known to be visceral afferents. These two potential components have characteristic physiological properties which permit their differentiation from the B2 and C components possessing properties of a much slower order. The fibers responsible for the B2 potential are the smallest thinly myelinated ones found in the nerve. Unmyelinated fibers give rise to the