E. H. McNally

Passage of ovoglobulins through the shell membrane.

It has been shown by Pearl and Curtis 1 that during the sojourn of the egg in the uterus the weight and nitrogen content of the albumen increases by the addition of a nitrogenous solution after the shell membrane has been formed. Data were collected to observe what kind of nitrogenous materials were added after the shell membrane was formed. Mature eggs to be used as controls were obtained in the morning from hens just beginning to lay a clutch of eggs, so that it was likely that they would lay the next day. Four to 6 hours after the egg was laid the hens were sacrificed and the immature eggs removed from the uterus. At this time the eggs were found with the shell membrane formed. The mature egg of the morning and the later immature egg from the same hens were analyzed as pairs. The eggs so obtained were separated into yolk, thick albumen and thin albumen. A screen, similar to that described by Holtz 2 and Almquist was used for the separation of the thick from the thin albumen. Thirteen pairs of eggs were separated in this manner. The results of the separation of the albumen and the yolk were found to confirm Pearl and Curtis in that only 60% of the albumen by weight, and 90% of the nitrogen in the albumen were present after the shell membrane was formed, and it was for the most part thick albumen. The albumens were diluted, the ovomucins were removed with the centrifuge, and the supernatant fluid was made up to volume with a small amount of sodium chloride or sodium sulfate present to prevent precipitation of the ovoglobulins. The ovoglobulins and the ovalbumins were separated by precipitation of the ovoglobulins with 1.5 M sodium sulfate by a technique similar to that of Howe 3 for blood serum proteins. Non-protein nitrogen was determined by using Almans tannic acid reagent or 2.12 sodium sulfate for protein precipitation. The ovomucoid content was determined by heat coagulation of the other proteins in the presence of acetate buffer approximately pH 4.7 and 0.2 M sodium sulfate. No attempt was made to separate the ovoglobulins or ovalbumins. Nitrogen was determined by macro-Kjeldahl.

Relative Amount of Mucin in Thick and in Thin Egg White

The white of a hens tgg is readily separated into two portions, the thin white and the thick white. The yolk appears to be floating in thin white enclosed in a sac of thick white and this thick white is suspended in another (outer) layer of thin white. 1 Previous studies of tgg white have not demonstrated the nature of the difference between thick and thin white. In studying the proteins of egg white we have found that the thick portion of the white contains a much higher proportion of a protein possessing the properties of mucin than the thin white. This protein is soluble in an excess of mineral acids, insoluble in an excess of acetic acid, has a low nitrogen content (12.9%), and has the general physical properties of mucn. Examination of the eggs of some other birds indicates that this unequal distribution of mucin is not confined to the egg of the hen. Table I shows the mucin content of the eggs of the hen, pigeon and duck. The whites of the eggs were separated on a screen as described by Hoist and Almquist. 2 The thin white separated by this method contains both the outer and inner thin whites. 1 Tests of the inner thin white indicate that it may contain only minute quantities of mucin. It is possible that in the formation of eggs the mucin secretion and the serous secretion are poured out together and that the mucin particles coalesce, holding a certain amount of thin white, and that the volume of thick white varies with the changes in hydrogen-ion concentration. Various authors, when discussing the preparation of the proteins of eggs, refer to the fact that they have dissolved egg white in salt solution or in water.