Mutual contact inhibition of extension of chick sensory nerve fibres in vitro

Methods were devised for measuring various aspects of the geometry of nerve fibre outgrowths from chick dorsal root ganglia in short‐term plasma clot cultures. Optical birefringence was used as a measure of the magnitude and direction of stresses which developed within the plasma clots during the incubation period. The data obtained indicated that contact guidance of nerve fibres, along fibrin micelles of the medium, is not of prime importance in determining the courses of nerve fibres in non‐fasciculated outgrowths. A mutual contact reaction, between nerve fibres, was observed using time lapse cine‐photomicrography, and the patterns of nerve fibre outgrowths could be largely attributed to such a reaction. This contact reaction is similar, in many respects, to contact inhibition of locomotion in cultured fibroblasts; and it is proposed that the reaction be termed “contact inhibition of extension.”