The addition of 1 · 10
–4 ouabain (strophantin-G), a Na
+-K
+-dependent ATP-ase inhibitor, to the cultivating medium of chick embryo spinal ganglia in vitro cultures caused the vacuolization of the cytoplasm of the fibroblast-like cells, but not of the nervous ones, after 6 h of culture, with a maximum after 24 h.