Cultures of V. cholerae produce a substance (F.F.) which causes shedding of the epithelium when pieces of guinea pig ileum are exposed to its action. F.F. can be demonstrated in culture filtrates only, and is absent in washed suspensions and autolyzates of V. cholerae. F.F. is heat-labile, inactivated by formaldehyde, exposure to 37 C and by ageing. Antigenically F.F. is very similar to, if not identical with the somatic antigen of V. cholerae. It differs from the somatic antigen in its physical characteristics.