On the Structure of a Hen's Egg Yolk and Yolk Spheres

Abstract

1. Yolk of a egg was fixed with 10% acrolein-0.05M phoshate buffer (pH 7.4) of LUFT11) by keeping in a cold dark place for 5-7 days and frazen sections of 3-7μ thickness, usually of 5μ, were prepared. Some of the sections were stained for lipid with Sudan IV or Sudan Black B-55% ethanol solution, 1% Nile Blue A solution, or BAKER'S acid hematein. Other sections were post-fixed with the HELLY solution and stained with Azan or extracted with pyridine and submitted to the SCHIFF reaction (acrolein-SCHIFF reaction).Experimental hens were given diet mixed with Sudan IV or Sudan Black B, or given intravenous injection of dye colloid solution, and the time the yolk spheres were formed was presumed from the striations of the dye formed inside the yolk.The shape of striped patteren of the dye in the yolk seemed to suggest that there might be a kind of potential flow in the growing yolk and a test was made with an electrical model. For the circuit, a KOHLRAUSCH bridge used in hydrodynamics was employed. A brass ring was provided with insulators corresponding to the blastodisc and a highresistance part corresponding to the periphery of the blastodisc, and 10% sodium chloride solution was filled inside the brass frame. An electrode was placed in the center of the ring, and a weak alternating current was passed to such a degree that there would not be any heat generation. Resistance in the high-resistance part was varied to obtain isopotential curves.2. White yolk spheres are distributed in latebra, neck of latebra, nucleus of Pander, and yolk surface layer around the blastodisc, and only yellow yolk spheres were observed in other parts. Yolk spheres in the surface layer of the yolk were medium to small yellow yolk spheres except around the blastodisc. Primordial yolk spheres were distributed from the center of latebra to the part adjacent to the blastodisc, becoming smaller as they approached the blastodisc and forming a vacuole in the inclusion and finally formed a mass of foams.3. White yolk spheres were varied in shape; from a primordial yolk sphere of 3-25μ diameter containing one drop-like inclusion to that of around 40μ containing numerous fine droplet inclusions. The inclusion substance tended to become smaller and more numberous with increase in the diameter of the spheres. On the other hand, yellow yolk spheres were 30-150μ in diameter and contained numerous fine granular inclusions, which were sometimes more coarse.There was no difference in the stainability of the inclusions of these two kinds of yolk spheres, and the staining indicated that the main component was a protein, with a small amount of phospholipid. Stainability of the matrix was also similar in the two spheres and indicated the presence of a large amount of fats besides the protein. Numerous fat drolets showing the characteristic of a neutral fat were observed but they were very fluid and their localization could not be clarified.The greatest difference between these two kinds of yolk spheres lies in the concentration of phospholipid in the matrix. While the matrix of white yolk sphere was almost negative or weakly positive to acid hematein, that of yellow yolk sphere was strongly positive to it.4. Layered structure was invariably seen in the latebra in which primordial yolk spheres and slightly large yolk spheres were arranged alternately. As a whole, the structure resembled the form of yellow yolk spheres nearer the outer layer. The layer of yellow yolk spheres in the outer side of the latebra showed layered changes in the degree of stainability but majority of hen eggs showed approximately uniform structure, irrespective of yellow or white yolk layer.5. The continuous phase between yolk spheres was fairly marked in the site where primordial yolk spheres were present and extremely small in the site with the other yolk spheres. Its staining characteristics indicated the presence of a small amount of protein.