Vitellus (U. S. P.)—Yolk of Egg.
Preparation: Glycerite of Yolk of Egg
"The yolk of the egg of Gallus Bankiva var. domestica, Temminck (U. S. P.) (Phasianus Gallus, Linné).
Class: Aves. Order: Gallinae.
SYNONYM: Ovi Vitellus.
Source.—The Common hen, or Dunghill-fowl, Gallus Bankiva (Phasanius Gallus), supposed to have been originally the jungle-fowl of India, is now domesticated almost everywhere. Its egg is the part used in medicine; less frequently the eggs of ducks and geese are in domestic use.
Description and Chemical Composition.—According to J. König (Die Menschl. Nahrungs- und Genussmittel, 3d ed., Vol. II, 1894, p. 201), the average weight of a hen's egg is about 53 grammes, the limits being from 30 to 70 grammes. It consists of the egg-shell with its lining membrane (11.5 per cent), the egg-white or albumen (58.5 per cent), and the yolk (30 per cent).
I. TESTA OVI (Putamen ovi, Egg-shell) is composed chiefly of calcium carbonate (89 to 97 per cent), calcium and magnesium phosphate (0.5 to 5 per cent), magnesium carbonate (0 to 2 per cent), and organic substance (2 to 5 per cent). The carbonate of calcium renders the shell absorbent and antacid. The albuminous membrane (Pellicula ovi, Membrana putaminis) which lines the inner surface of the shell, is a keratin- (horn) like substance, soluble in alkalies, from which solution it is precipitated by acids. At the broad end of the egg it forms an air space, the Follicula aëris.
II. ALBUMEN OVI (the White or Glaire of egg, Ovalbumen) is an almost colorless, transparent, odorless, liquid mass, consisting of a thin, alkaline fluid, rendered viscous on account of being enclosed in cells forming a network of delicate membranes. This fluid contains on an average 85.75 per cent of water, 12.67 per cent of nitrogenous matter, 0.25 per cent of fat, and 0.59 per cent of salts, which consist for the most part (about 92 per cent) of the chlorides of potassium and sodium. The yolk of the egg (see below) has a markedly different composition. The albumen of the white of egg (ovalbumen) corresponds to the formula C144H122N18S2O44 (See J. König, loc. cit.), containing 1.6 per cent of sulphur. This element is partly liberated in the form of hydrogen sulphide when the egg decomposes. Ovalbumen, however, is not a simple compound; its chief constituent is ovalbumin, probably a mixture also; it is soluble in water, and coagulates by exposure to a temperature of 60° to 70° C. (140° to 158° F.). It is precipitated from aqueous solution by the addition of alcohol, hydrochloric acid, excess of sodium sulphate and ammonium sulphate, not by sodium chloride, and forms precipitates with tannic acid, creasote, mercuric chloride, salts of copper, chlorides of gold and tin, the acetates of lead, potassium ferrocyanide in acetic acid solution, etc. It is not precipitated by concentrated solution of magnesium sulphate at 20° C. (68° F.), and may be separated by means of this behavior from ovoglobulin, another nitrogenous constituent of the egg-white, forming about 0.67 per cent of the latter. Ovomucoid is a mucous substance rich in nitrogen (12.65 per cent) and sulphur (2.2 per cent), also contained in ovalbumen. (For further details regarding these albuminous compounds and their reactions, see Hammarsten and Mandel, Physiological Chemistry, 2d ed., 1898, pp. 410-416, or similar publications.)
The reactions of ovalbumen differ somewhat from those afforded by seralbumen, or the albumen contained in the serum of the blood; unlike seralbumen, ovalbumen in aqueous solution is precipitated by ether and concentrated hydrochloric acid, and both differ somewhat from the albumen in the urine accompanying Bright's disease. To test a specimen of urine for albumen, apply the exceedingly sensitive Heller's test, as follows: Place 3 Cc. of strong nitric acid into a test-tube, add 1 Cc. of water, cool, and carefully filter into this liquid the urine, employing two layers of filtering paper, and taking care that the urine runs down the sides of the test-tube and forms a layer above the nitric acid. If albumen is present, a white ring is formed at the zone of contact. This test in case of a positive result may be supplemented by the heat test: Slightly acidulate the urine if alkaline with acetic acid, filter, if necessary, through a double filter into a test-tube, add about one-tenth its volume of a saturated solution of sodium chloride, and heat the upper part of the liquid over a small flame; if a cloudiness appears, which is not dissolved after cooling by the addition of nitric acid (phosphates), the turbidity will be due to albumen.
When the white of eggs is placed in thin layers on glass, and dried in the air, it becomes solid without losing its transparency or property of dissolving in water, and may be preserved in this manner for a long time; these dried fragments (albumen ovi siccum) will be found to answer as a substitute for the original white, when formed into a solution with water. They are insoluble in ether or alcohol. White of egg kept in its original condition speedily decomposes.
III. VITELLUS OVI, the Yolk of egg, is enclosed within a fine membrane, and consists of minute cells holding albuminous matter with yellow oil. It becomes solid (coagulates) by heat. Triturated with water, yolk of egg produces a thick, opaque solution, much used in pharmacy for suspending oily and resinous substances in the former fluid. Heat solidifies it, and its oil (oil of eggs) may then be obtained by expression; or, the oil may be prepared by boiling the yolk hard, then digesting it with ether or alcohol, filtering and distilling off the solvent, when the oil remains. When extracted by means of ether, it contains chiefly triolein (about 83 per cent), solid fats (about 16 per cent), cholesterin (1.6 per cent), lecithin (0.2 per cent), and coloring matters (M. Kitt, Pharm. Centralhalle, 1897, p. 340, from Chem. Zeitg.). J. König (loc. cit.) gives the following average composition of the yolk of eggs: Water, 51.8 per cent; vitellin, 15.8 per cent; nuclein, 1.5 per cent; palmitin, stearin and olein, 20.3 per cent; the crystallizable alcohol, cholesterin (C26H44O), 0.4 per cent; glycero-phosphoric acid, 1.2 per cent; lecithin, 7.2 per cent; cerebrin, 0.3 per cent; coloring matters (luteines) 0.5 per cent; salts, 1.0 per cent, consisting chiefly of phosphates of calcium, potassium and sodium. Vitellin (of Gobley) is a peculiar albuminous body, resembling the albumins of the globulin group (see Hammarsten and Mandel, loc. cit.); like these, it is insoluble in water, but is soluble in a 10 per cent sodium chloride solution, from which it is precipitated by dilution with water. It coagulates at a temperature of 70° to 75° C. (158° to 167° F.). Lecithin, a rather complex waxy compound occurring also in the brain, nerves, muscles, blood, etc., was first obtained by Gobley from the ether extract of the yolk. Its molecule combines the radicals of glycerin, phosphoric acid, oleic acid, palmitic acid and the base choline (C5H14NO2) (see under Trimethylamine). When boiled with baryta water, it is split into the above-named fatty acids, glycero-phosphoric acid and choline.
Eggs may be preserved for some time by coating them with wax, gum, fat, paraffin, linseed oil (recommended by Violette), or similar substances, which render the shell impervious to water and air. Packing the eggs in salt or milk of lime, placing the pointed end downward, has been common practice. (Also see J. König, loc cit., and Amer. Jour. Pharm., 1899, pp. 7 and 24.)
Action and Medical Uses.—Eggs have been much employed in medical practice. The shells, when reduced to a very fine powder, may be used in acid conditions of the digestive organs, in the same doses as prepared chalk. The albumen or white is useful as a demulcent in diseases of the intestinal mucous membrane, and is a valuable agent in the treatment of poisoning by bichloride of tin, the soluble salts of copper, and bichloride of mercury; its efficiency in these cases is owing to its combining with the oxide or chloride of the metal, forming comparatively harmless compounds. In cases of redness or excoriation from pressure, it forms a good local application, when used in the form of a liniment, made by agitating it briskly with its own volume of alcohol. It is also employed as a clarifying agent for wines, and some other liquids. Its efficacy depends on its coagulation, by which it entangles in its meshes the impurities with which it either rises to the surface or precipitates. When the liquid to be clarified does not spontaneously coagulate the albumen, it is necessary to apply heat (P.). The white is also used for diffusing throughout water substances which are not dissolved by it. Mixed with a small quantity of alum, a coagulum (alum curd) is formed which has been found efficient as a local application in some inflammations of the eye, after the more severe symptoms have been subdued. It is likewise valuable in this form for the treatment of erysipelas, scalds, and burns, and poisoning by rhus when located near the eyes. The yolk is a mild nutrient, and generally does not offend the stomach; added to an infusion of ginger, and thoroughly beaten up with it, it has been found serviceable in dyspepsia. It answers the purpose much better than the white in the preparation of mixtures, emulsions, etc. Its powers as an antidote to poison are the same as those of the white. Contrary to the generally accepted notion, the hard-boiled yolk is easy of digestion. The oil obtained from the hard-boiled yolk has been found serviceable in cracked nipples. A non-collegiate practitioner in this country acquired some celebrity in the treatment of dyspepsia, loss of appetite, constipation, hemorrhoids, etc.; the agent he employed was a powder composed of equal parts of the inner skin of chickens' gizzards (ingluvies pulli), dried and pulverized, sulphur, and resin, of which from 5 to 10 grains were to be taken 3 or 4 times a day (see Ingluvin).
An artificial serum has been used to moisten the hands with during the manipulation of the abdominal contents while operating for removal of the ovaries, etc., and for other purposes; it is composed of common salt, 1 drachm; white of egg (albumen) 1 1/2 drachms; pure water, 1 pint. Mix. During an operation in which this fluid is employed it should be constantly maintained at a blood-warm temperature. White of egg forms a good cement for mounting certain specimens for microscopic investigation.