Growth and Development of Chick Embryos Nourished by Fractions of Yolk

To determine the nutritional value of yolk fractions to chick embryos, salts-glucose solution was used to displace yolk from fertile eggs incubated for 4 days, leaving embryos and membranes nearly intact. Embryos were then given no supplement (negative controls), 1.5 ml yolk/egg (experimental controls), or one of 3 yolk fractions obtained by centrifugation: sedimented granules, supernatant plasma, or a floating fraction from the supernatant. Fractions were given as either the amount from, or an amount isonitrogenous with, 1.5 ml yolk. During the 4.5-day experimental period, negative controls survived 69% as well as experimental controls, but grew only 40% as large. Granules increased weight only slightly, but permitted normal survival; supernatant plasma more than doubled weight, but decreased survival below that of negative controls. Floating fraction permitted excellent survival and growth, although embryos were anemic. The phosphoprotein phosvitin and some components of the lipoprotein lipovitellenin were seen by electrophoresis to disappear from yolk sacs during incubation. Lipovitellenin appears to have been the best-utilized fraction during the experimental period.