The effects of embryonic pars distalis grafts and albumen on the growth of chick embryos.

Normal chick embryos swallow and utilize the albumen in the egg between the 11th and 15th day of incubation (Witschi, 1949). They use approximately two-thirds of the yolk by the end of incubation (Romanoff & Romanoff, 1949). Thus the embryo has access to 4 g of protein in the albumen and 3 g of protein in the yolk (Romanoff & Romanoff, 1949). Embryos which have been hypophysectomized by partial decapitation, which is the only practical way of hypophysectomizing chick embryos (Betz, 1965 a, see also the reviews of Benoit (1962) and of Hinni & Watterson (1963), do not develop an upper beak and do not swallow much of the albumen since most of it remains in the egg (Witschi, 1959; Betz, 19656). The rate of growth of hypophyseoprivic embryos between the 14th and 18th day of incubation is reduced to 53 % of the normal rate (Vogel, 1965). At 18-5 (Thommes, 1967) and 20 days of incubation (Fugo, 1940; Case, 1952; Betz, 1967) these embryos are only one-half as heavy as normal embryos. These results contradict those of Wolff & Stoll (1937) and Stoll (1939). Witschi (1959) said, in comparing the body weight of normal and hypophysectomized embryos, ' . . .it is evident that obstruction of alimentary intake must dwarf the fetus from the 1 lth day on. On the other hand, if the albumen is swallowed the chick must gain weight even if the albumen were not assimilated. Therefore, the question of somatotrophic hormone (STH) deficiency remains undecided'. Thommes (1967) reported that pars distalis grafts restored the body water content of hypophysectomized chick embryos to normal by 18-5 days of incubation if the data were expressed as the ratio of grams of water in the body to grams of dry body weight; however, both the wet and dry body weights were subnormal. Betz (1967) reported that most of the characteristic defects of hypophysectomized chick embryos are prevented by pars distalis grafts. Even though the growth of these embryos is improved it is still subnormal. Thus, the limited growth of these embryos may be due either to reduced albumen ingestion or failure of the pars distalis grafts to produce normal amounts of STH and other hormones.