Abstract
1. Sympathetic and dorsal root ganglia from young mice and new-born rats were cultured in vitro. The activity of the outgrowing Schwann cells was studied with time-lapse photography.2. Schwann cells exhibited a pulsatile activity with a contraction rate varying from 1 to 12 min. The occurrence of pulsations depended on the mode of attachment of cells to their surroundings.3. Fibres of various materials were introduced into the cultures in an attempt to simulate conditions obtaining in vivo. Schwann cells attached themselves to these fibres and rotated about them depositing myelin. Polarized light and histochemical studies showed that myelin was formed as early as four days in vitro.4. The possible significance of the behaviour of Schwann cells in vitro is discussed.