When a peripheral nerve is crushed with forceps the myelin and axoplasm are displaced along the nerve and behave as liquids. The direction of this displacement can be controlled by obstructing the flow in one or the other direction. After the pressure on the nerve has been released there is a return flow of myelin and axoplasm, refilling the crushed region. The displaced axoplasm and myelin become mixed. During the return flow they again separate to give the appearance of normal fibres, before they undergo Wallerian degeneration. Between 24 and 48 h after the crush there are changes in the distribution of the myelin at the nodes. The ends of the nerve fibres proximal to the crushed point, that is, in continuity with the nerve cell body, become larger than those at the distal ends.