Fast and Slow Phases of Axoplasmic Flow in Ventral Root Nerve Fibres¹

The pattern of activity found in ventral roots removed at different times after seventh lumbar and first sacral cord injections of [ 3 H]leucine gave evidence for fast and slow phases of axoplasmic flow. An intra‐axonic location was shown for the fast flow by the block of downflow produced by freezing a narrow region of the ventral root, by reduction of downflow on preinjection of puromycin into the cord and by radioautography of ventral roots. Separate mechanisms appear to be required to account for the fast and slow phases of axoplasmic flow.