Albumen absorption during chick embryogenesis.

In birds albumen represents a substantial part of the reserve material for their embryological development (Romanoff & Romanoff, 1949). In Gallus gallus albumen proteins form 50 % of non-incubated egg protein content (Romanoff & Romanoff, 1949). During incubation such material is absorbed and utilized, to a great extent, for the synthesis of embryonal proteins (Fiske & Boyden, 1926; Rupe & Farmer, 1955). It is not yet well understood how these processes (albumen absorption and utilization for the energetic and nutritional needs of the embryo) take place. The present available data indicate that the amount of albumen solids begins to diminish starting from 11 to 12 days of incubation (Romanoff & Romanoff, 1933; Rupe & Farmer, 1955). From 13 to 14 days, after the seroamniotic connexion perforates, the protein content of the amniotic fluid shows a marked increase because of the passage of albumen (Needham, 1931; Romanoff, 1960). During the same development period albumen proteins can be recovered, in large amounts, in the yolk (Saito, Martin & Cook, 1965; Carinci, Wegelin & Manzoli-Guidotti, 1966). Indeed the major part of albumen is very likely absorbed across the yolk and the amnion. In this connexion the function of the albumen sac is still not clearly known. This sac, formed starting from the 9th to 10th day of incubation by a folding of the chorioallantois, is considered by some authors to be responsible for albumen absorption (Patten, 1950). During development, the protein composition of the residual albumen remains substantially unchanged and very similar to that of the non-incubated egg (as judged by paper and free-boundary electrophoresis) (Marshall & Deutsch, 1950; Rizzoli, 1956); besides, the immunological behaviour of the individual proteins is unmodified (Kaminski & Durieux, 1954). The electrophoretic data indicate also that the relative proportion of different albumen proteins is constant during incubation (Marshall & Deutsch, 1950), though some quantitative observations demonstrate a relative diminution in ovalbumin concentration (Hasegawa, Taguchi & Hasegawa, 1956). Less is known about the protein composition of amniotic fluid (Kaminski & Durieux, 1954; Geelhoed & Conklin, 1966).