A phase contrast and time lapse cinematographic study of normal mouse sciatic nerve cultured in vitro was made. The Rose chamber and chicken plasma clot methods were employed. The growth was characterized by three basic cell types: a spindle-shaped cell with a bulging nucleus, a racket-shaped cell with a short wide fan-shaped process and an opposite filiform process, and a kite-shaped cell with abundant ectoplasm. The spindle-shaped cells exhibited a pulsatile rhythmic activity. The rhythm of contraction varied from two to eighteen minutes. No contractile activity was observed in the case of the racket-shaped cells nor in the kite-shaped cells. The spindle-shaped cells were thought to be Schwann cells, the kite-shaped cells were considered of a fibroblastic nature, whereas no source could be found for the racket-shaped cells, although the perineurium was considered as a possible origin. The cultures were maintained up to 80 days, but at no time were phagocytes, observed. With the methods employed no transformation of cells from one type to another took place, and the Schwann cells did not transform themselves into phagocytes.