Olfactory nerve of Carassius auratus, a river fish common in Japan, is consisted of two bundles of non-medullated nerve fibers. Two waves were seen in the action potential of the nerve, in the cathode ray oscillograph. The conduction velocity of the first wave was faster than the second, but the excitability of the former was lower than the latter. These facts show the existence of two kinds of fibers, i. e. fast and slow, in olfactory nerve. From the wave form of the action potential, it was elucidated that the large bundle of nerve contained both fast and slow fibers, but the small bundle contained only the fast one.
