“…More valuable information has been obtained by the experimental induction of embryonic death at known stages of pregnancy. Various methods have been employed, such as the administration of natural oestrogens (Parkes & Bellerby, 1926;Smith, 1926;Parkes, 1930;Newton, 1935 ;Huggett & Pritchard, 1945) or synthetic oestrogens (Parkes, Dodds & Noble, 1938;, colchicine (Kerr, 1947), gonadotropins (Engle & Mermod, 1928;Huggett & Pritchard, 1945) vitamin E deficiency (Evans & Burr, 1927 ;Urner, 193 I) and mechanical interference (Giacomini, 1892 ;Hammond, 1917;Newton, 1935;Courrier & Gros, 1936;van Wagenen & Newton, 1943;Huggett & Pritchard, 1945;Pritchard & Huggett, 1947;). Administration of oestrogens or colchicine appears to result in the death of the membranes as well as the embryos, whereas the membranes may survive the destruction of the embryo by vitamin E deficiency or mechanical interference.…”