“…However, they regarded this as evidence for an active group in the protein molecule, which was still regarded as the pure hormone. Anselmino, Hoffman andHerold in 1933 andTyslowitz in 1943 reported the ultrafiltration of AW activity. This work was confirmed and ex tended in our laboratory and it was found that both AW and AA activity would pass through a membrane impermeable to substances of molecular weight 13,000.…”