vitellus - Wiktionary vitellus vitellus ‎( countable and uncountable , plural vitelli or vitelluses ) (biology) The contents or substance of the ovum ; egg yolk . 1861, F. Rymer Jones, The General Structure of the Animal Kingdom (page 48) In the sarcodo there takes place a process which may be in some measure compared with what occurs in the vitellus after the fecundation of an ovum. The granules becoming united together form groups, which soon divide and subdivide […] (botany) Perisperm in an early condition. Image Partager l'image Voici le code HTML déjà fait, pour voir cette image sur votre site web : <a href=""><img src=" Interior view of a bird egg.jpg" border="1" alt="Egg"></a><p><a href="">Egg</a> - <a href="">Visual Dictionary</a> - Copyright © 2005-2016 - All rights reserved.

Voici le code UBB déjà fait, pour voir cette image sur votre Forum : [img] Interior view of a bird egg.jpg[/img] [url= - [url= Dictionary[/url] - Copyright © 2005-2016 - All rights reserved. Interior view of a bird's egg: hard, porous shell enclosing an embryo and the substances that nourish it during incubation. Shell: hard crust covering and protecting the egg. Developing embryo: small pocket related to the germ. Air space: part of the egg containing only air. Vitellus or yolk: part of the egg which develops into an embryo once the egg has been fertilized. Albumen or white: white of the egg, which nourishes the embryo once the egg has been fertilized. Amniotic liquid: liquid substance in the amnion. Embryo: bird which has not yet hatched. Allantoic fluid: one of three extensions of a bird embryo. Shell membrane: membrane on the inside of the shell. Chalaza: part of the white of the egg.

Vitellus | Define Vitellus at Dictionary.com vitellus [vi-tel-uh s, vahy-] /vɪˈtɛl əs, vaɪ-/ Spell the yolk of an egg. Origin of vitellus Examples from the Web for vitellus Expand Historical Examples This vitellus or yolk undergoes a series of segmentation or dividings which are known as spontaneous segmentation. British Dictionary definitions for vitellus Expand noun (pl) -luses, -li (-laɪ) 1. (zoology, rare) the yolk of an egg Word Origin C18: from Latin, literally: little calf, later: yolk of an egg, from vitulus calf Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012 Vitellus (U. S. P.)—Yolk of Egg.

| Henriette's Herbal Homepage Henriette's Herbal Homepage Welcome to the bark side. Search form Vitellus (U. S. P.)—Yolk of Egg. Botanical name: "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 ½ 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. What is a Chicken Egg? (with pictures) What is a Chicken Egg?

Last Modified Date: 28 November 2016 Copyright Protected: Top 10 facts about the world An egg is a vessel that contains an ovum — the reproductive cell produced by a female that would nurture and sustain an embryo . A chicken egg is the egg laid by a chicken. In general, eggs are composed of several parts: they have a hard outer shell, which would help protect a growing bird embryo (if the egg is fertilized); and inside the shell is the ovum. In a fertilized egg, a chick grows inside the egg for about 21 days before it is strong enough to break out of the shell and become a “fully-fledged” chicken. In most mammals , ova that are unfertilized are periodically shed with the special lining of the uterus that would help nurture a growing fetus . Fertilized ova stay in place and become part of the building blocks that grows into an infant mammal. Chicken eggs are different in this respect, since hens lay both fertilized and unfertilized eggs, and most of the development of the chicken embryo in fertilized eggs occurs outside of the hen’s body. Special care of a fertilized egg is required for a chick to grow and hatch.

There are two main components of the ova in chicken eggs: the albumen or “white” of the egg and the vitellus or yolk. Most people will note some thick milky white membranous structures in the egg too. When not providing nutrition for growing chickens, these eggs are a source of nutrition for people and for animals that eat them. In fact, of all eggs consumed by people, those from chickens are most common, and recipes calling for eggs tend to mean ones from hens, unless they specify otherwise. Though there are specialty markets that sell emu , ostrich , quail , and duck eggs, these remain a tiny percentage of most eggs purchased by humans. While the chicken was once hailed as perhaps a perfect food for humans, there are some concerns about consuming too many eggs. Though a single egg isn’t tremendously high in calories, the yolks do contain high levels of cholesterol . Some people avoid this issue by simply eating egg whites instead, which are high in protein, although not everyone enjoys eating the whites alone. There’s also some argument that sources of cholesterol in egg yolks may actually help lower overall bad cholesterol count, though this issue is debated.

Most people stick to eating the interior of the egg and either discard or compost the shells. Actually, eggshells are edible, and some people blend them into shakes. Eggshells may also constitute part of chicken feed since they have nutritive value. Different breeds of chickens lay eggs of different colors, but this has no direct impact on the taste or nutritional value of the egg itself. One thing that may prove confusing for people is the different grades of chicken eggs and their different sizes. Eggs come in peewee, small, medium, large, extra-large, and jumbo in the US, although "large" is the most common size used. Moreover, some eggs are labeled organic and others may be sold as created by free-range chickens. The country in which the eggs are produced usually regulates the definitions of each of these terms and grades. Typically, free range and organic eggs will cost most, but the price is usually higher for larger eggs too. Some people purchase fertilized eggs because they’re lower in cholesterol. Ad SarahSon Post 11 My dad grew up on a farm where they had a lot of chickens. They would gather the eggs, and whatever wasn't needed for their family, they would sell.

This is something that many farm families still do today. I have always been kind of afraid of chickens and don't know how comfortable I would be reaching in and grabbing the eggs. This article also reminds me of the age-old question of which came first, the chicken or the egg? golf07 Post 10 It doesn't seem like you hear as much any more about how chicken eggs are so high in cholesterol. Is it the yolk that gives them the high cholesterol content? I always thought eggs were full of good nutrition, and a cheap meal when I was a poor college student. sunshined Post 9 I feel very fortunate to have a neighbor who sells farm fresh chicken eggs. I don't think she can consider them organic or even free range, but I can see how they are fed and taken care of, and feel safe buying eggs from her. I don't usually have any problem getting as many eggs from her as I need. If there is a big salmonella scare though, people are afraid to buy eggs in the store, and sometimes she runs out of them. andee Post 8 I grew up on the farm and was used to eating brown eggs with bright yellow yolks.

Whenever we had overnight guests, they always commented on how yellow our eggs were. I always thought that was a funny comment because that is all I had ever known. Not until I moved to the city and began buying eggs in the store did I realize what they meant. I also realized that the shells on our chicken eggs at home were much thicker and harder to crack. Now I go out of my way to buy brown eggs that are either organic or free range. Some stores carry them, and I can also find some at farmers markets. Sure, I pay more for a dozen of them, but overall, eggs are still pretty cheap when you consider how much nutrition and protein you are receiving from them. giddion Post 7 @kylee07drg – The easiest way is to use a funnel. My friend taught me this trick a few months ago, and it has opened up a whole new world of recipes to me, because I had the same problem as you. The yolk is too large to go through the narrow hole in the funnel. However, the egg white will slip right on through. Just be sure you have a mixing bowl beneath the funnel to catch the egg white.

kylee07drg Post 6 So many recipes, especially desserts, call for egg whites. I have always had trouble separating them from the yolks, so I just avoid these recipes. Can anyone tell me what the best way to separate an egg white from a yolk is? I can't do it using just the shells like some people can. seag47 Post 5 Some people think it's a little weird to cook chicken and eggs together, but I do it all the time. I dip raw chicken in eggs and milk before rolling it in seasoned flour and frying it. My husband also makes an excellent chicken teriyaki meal that uses both chunks of chicken and bits of scrambled egg. It's so delicious, and you might not think this would be true, but chicken and eggs taste great together! healthy4life Post 4 My mother actually got to witness hatching chicken eggs when she was young. Her family raised their own chickens, and they ate some of the eggs, but the ones they didn't eat got to develop into more chickens. It seems a little unsanitary to eat something that a chicken has been sitting on top of for awhile. I try not to think about this while eating scrambled eggs!

DFMeyers Post 2 @liveoak- I know what you mean about not having a clue about eating the shells. I could even grind up the shells into a powder and put them in soups or other foods. I will also think about how I am going to use the shells the next time I buy eggs. liveoak Post 1 I had no idea that you can eat the shell of an egg. I always thought that they should just be thrown out. To think I have been throwing out something with nutritional value all these years is kind of sad. The next time I see chicken eggs for sale I will definitely try eating the shell in a shake. Post your comments What does vitellus mean? definition and meaning (Free English Language Dictionary) vitellus; yolk Hypernyms ("vitellus" is a kind of...): food ; nutrient (any substance that can be metabolized by an organism to give energy and build tissue) Holonyms ("vitellus" is a part of...): egg (animal reproductive body consisting of an ovum or embryo together with nutritive and protective envelopes; especially the thin-shelled reproductive body laid by e.g. female birds) Learn English with...

Proverbs of the week "It's better to have loved and lost than never to have loved at all." (English proverb) "When a man moves away from nature his heart becomes hard." (Native American proverb, Lakota) "The day of happiness is short." (Arabic proverb) "Whilst doing one learns." (Dutch proverb) Page delivered in 0.0392 seconds AudioEnglish Definitions... Just One Click Away! Now you can lookup any word in our dictionary, right from the search box in your browser! Click here to add the AudioEnglish.org dictionary to your list of search providers. Ovi Albumen. Egg Albumen. Ovi Vitellus. Yolk of Egg. | Henriette's Herbal Homepage Ovi Albumen. Egg Albumen. Ovi Vitellus. Yolk of Egg. Botanical name: EGG ALBUMEN. Synonyms.—Albumen; White of Egg. Egg albumen is the liquid white of the egg of Gallus Bankiva, var. domesticus (Order Gallinae).

It occurs as a glairy, viscid, usually colourless, but occasionally pale yellow, liquid; almost tasteless, or having only a faint saline taste; soluble in water, but insoluble in alcohol or ether. It consists of a semi-fluid material, which is pervaded by a network of firmer and more fibrous nature, closely resembling the membrane enclosing the vitreous humour of the eye. On heating the aqueous solution to 75° it becomes coagulated. It is precipitated by most mineral and some organic acids, but not by phosphoric or acetic acid. Alcohol coagulates it, and ether precipitates it, the precipitate being only partially soluble in water. It is soluble in caustic alkalies, but forms precipitates with the salts of most of the heavy metals, e.g., mercury, copper, etc. It is precipitated also by volatile oils, camphor, phenol, and tannic acid. Its aqueous solution is laevorotatory.

When allowed to putrefy, it gives rise not only to amino-acids but also to other aromatic and fatty acids (e.g., butyric acid), indol, skatole, and cresol, and also to the alkaloid-like ptomaines. Egg albumen should be free from any unpleasant odour. Albumen Siccum, or dried albumen, may be obtained by careful evaporation on glass plates at a temperature not above 50°. It occurs in yellowish, transparent flakes or scales of a horny consistence. It is nearly soluble in about 10 parts of water, forming a neutral solution, which should respond generally to the description and tests given above. It should be free from unpleasant odour or taste. Constituents.—The semi-fluid portion of egg albumen is alkaline, and contains 82 to 88 per cent. of water, about 12 per cent. of proteins (globulins and albumins), 0.5 per cent. of sugar, traces of fats, alkaline soaps, lecithin and cholesterol, and less than 1 per cent. of inorganic residue.

The total average weight for one egg is 24 grammes (371 grains). On complete incineration, it yields on an average about 0.65 per cent. of ash, which consists of 42 per cent. of potassium chloride, 9 per cent. of sodium chloride, phosphates and sulphates of the alkalies, together with some silica, lime, iron, and magnesium. The organic portion has the elementary composition, carbon 53.7 per cent., nitrogen 15.5 per cent., hydrogen 7.1 per cent., oxygen 22.1 per cent., sulphur 1.6 per cent. The manner in which sulphur is contained in the molecule is unknown; its presence may be shown, however, by boiling the egg albumen with an alkaline solution of lead oxide, when lead sulphide is formed. By the action of the gastric juice, or pepsin in very dilute hydrochloric acid, albumen is converted into acid-albumin or syntonin, and finally into peptone.

Solution of egg albumen is prepared by mixing egg albumen by trituration with four times its volume of distilled water, and filtering through clean tow, previously moistened with distilled water; it should be recently prepared. Uses.—Solution of egg albumen with boric acid is sometimes used as a dressing in surgery. A solution of egg albumen made by dissolving the white of one egg in 150 mils (5 fluid ounces) of boiled and cooled water, adding salt to taste, and a little brand if necessary, is used in the diarrhoea of infants. OVI VITELLUS. YOLK OF EGG. Yolk of egg is obtained from the egg of Gallus Bankiva var. domesticus (Order Gallinae). The yolk of the egg is a membranous sac, enclosing a yellow, or reddish-yellow, opaque, odourless liquid, with a bland taste and alkaline reaction. The liquid is a natural emulsion of a yellow oil, which is suspended in water by the aid of albuminous matter. Constituents.—It contains about 16 per cent. of vitellin and other proteins, 11 per cent.

of lecithin, and 23 per cent. of fats. Uses.—Yolk of egg is employed as an emulsifying agent for oils, being particularly useful in the case of oil of turpentine and other limpid volatile oils. For this purpose it should be triturated lightly in a mortar, the oil being added by degrees, with a little water if necessary. One yolk will, as a rule, emulsify 3 to 4 fluid ounces of fixed oil. (See Emulsiones.) vitellus - definition of vitellus in English | Oxford Dictionaries Definition of vitellus in English: vitellus [mass noun] The yolk of an egg or ovum.

Example sentences ‘In no case, when comparing embryos from the same uterus, was the presence of vitellus found in only part of the embryos observed; neither was it found in small quantities.’ ‘Fish eggs can be round with the hook passed through or half round with the egg vitellus in the form of colored yarn waving out the flat side along the shaft of the hook.’ ‘With a center core, the darker core areas appear like fish egg vitellus and crustacean inner organs.’ ‘If eggs of Echinarachnius be inseminated with thin sperm suspension they throw off membranes that are fully formed and equidistant from the surface of the vitellus in from two to three minutes.’ Origin Early 18th century: from Latin, literally yolk. Pronunciation: Which of the following does a muso like? music Which of the following does an arctophile like? polar bears Which of the following does a philatelist like? fashion Which of the following does a logophile like? maths Which of the following does a bibliomane like? books Which of the following does an oenophile like? films Which of the following does a coleopterist like?

daisies Which of the following does a philhellene like? Irish culture Which of the following does a shutterbug like? photography Which of the following does a gricer like? gardening You scored /10 practise again? Retry Most popular in the world Australia Boiled Eggs: Soft and Hard — Part 1 :: ChemViews Magazine :: ChemistryViews Magazine: Boiled Eggs: Soft and Hard — Part 2 1. The Perfect (Boiled) Egg for Breakfast Boiling the breakfast egg to perfection is far from child’s play. On the way from hen to breakfast table, so many complex chemical processes must take place that the outcome of the cooking phase cannot always be precisely predicted. It will, therefore, be worth our time to examine more closely the oological-chemical fundamentals of cooking eggs in order to avoid insofar as possible — and with the aid of solid scientific information — both disappointment and family crises around the breakfast table. Figure 1. Soft-boiled egg in an egg cup, ready for breakfast, with typical (German) commercial markings.

In many parts of the world, a freshly boiled (usually soft-boiled) egg is the crowning touch to every breakfast table, and is the very embodiment of a good start to the day. When we rap a knife on the white or brown shell of such an egg we are seldom conscious of what a technical marvel we are dealing with (Fig. 1). Under that unpretentious eggshell (which in itself is a structural masterpiece!) is concealed, in the narrowest of spaces, a fully-fledged culinary delicacy, one that deserves very close examination (Table 1). Table 1. A hen’s egg typically weighs about 60 g, has a surface area of 53 cm2, and consists of a shell 0.3–0.4 mm thick weighing about 6 g, 34 g of egg white, and 19 g of yolk. The individual components are made up as follows [1]. We will now delve into more details regarding egg production, and into typical national food regulations, using the case of Germany as an example (see: " Egg Output Data and Food Regulations Applicable in Germany "). It is appropriate that we start at the ultimate source, the hen.

It is convenient that there is absolutely no need for us here to confront that age-old question “Which came first, the chicken or the egg?”, because none of the eggs on the market will have been fertilized. They are thus utterly incapable of generating either hen or rooster. 2. In the Beginning Was the Hen All modern chickens are thought to be descendants of the red junglefowl (Gallus gallus), and more specifically from the Javan subspecies (G. g. Bankiva; Fig. 2), probably hybridized to some extent with the grey junglefowl. G. g. Bankiva still exists in the wild in Indonesian and Indian forests. Countless of these birds were carefully bred over the ages to improve their meat, or their ability to lay many eggs; some birds were also bred for show purposes, either because they were especially handsome, or because they were unusually aggressive, lending themselves to a very dubious form of entertainment. Figure 2. A bankiva hen. Characteristics prized in laying hens are their derivation from light- or medium-weight predecessors and they are now capable of producing as many as 280 eggs annually.

One can only tip one’s hat to the breeders — and of course to the hens themselves! — considering that their bankiva hen ancestors typically laid only 8–12 eggs per year! Production of a 60 g egg by a hen weighing roughly 1.7 kg represents an incredible biosynthetic feat. Such a laying achievement presupposes optimal environmental conditions and a diet rich in protein and calcium, one that can best be appreciated after translation into human terms. That is to say, one would need to imagine a person producing an egg weighing 2 kg (i.e., ca. 4.5 lb) almost every day, supported by an almost daily food intake of 4 kg (nearly 9 lb) of highest-quality nutrients! Professor Waldemar Ternes, University of Veterinary Medicine Hannover, Germany, has suggested an even more dramatic comparison: the metabolic work accomplished by a hen in the course of ten days would correspond to a human being recreating his or her entire complement of arms and legs in the same time period. 3.

The Composition of a Hen’s Egg We now trace the path to the creation of a hen’s egg, with the associated phenomenal biosynthetic performances achieved by a laying hen [1–4] (Fig. 3). Figure 3. From ovary to egg. Modified schematic view based on Solomon [5]. t = 0 h: Ovulation A hen’s ovary is the site where every 7–10 days there occurs maturation of one of the over 3000 egg cells (ova) initially present. Ovulation entails rupture of the thin follicle of such a cell, allowing the free ovum to drop into the infundibulum (see Fig. 3). At this point the ovum has a diameter of about 4 cm, and it embodies 30–33 % of the total weight of the eventual egg. The fat-in-water emulsion (water content ca. 50 %) of this “egg-to-be” already includes nearly all the fat and cholesterol found in a mature egg. The vitellus or “yolk” contains, among other things, “yolk spheres”, 20–40 µm in diameter, whose structure is maintained even upon heating.

Our tongue, an extraordinarily sensitive tactile organ, is able to feel out this substructure, which in turn is what confers upon the yolk of a hard-boiled egg its “mealy” character. Lipovitellin, at 70 %, constitutes the chief lipoprotein of egg yolk; others include phosvitin (11 %) and what is known as the LDL or “low-density lipoprotein” fraction (12 %). Taken together the lipoproteins (66 %) lead to a yolk being the most fat-rich part of the egg as a whole. The terms low- and high-density lipoprotein (LDL and HDL) here refer exclusively to the sizes of the lipoproteins themselves. In other words, this has nothing directly to do with so-called “bad” (LDL) and “good” (HDL) cholesterol, since the latter refer to proteins in our blood, ones to which cholesterol is bound. Consumers often believe erroneously that a robust yellow color for an egg yolk is a measure of quality.

In truth there is absolutely no relationship between yolk color and freshness, or general husbandry of the hens, nutritional value, or flavor. The yellow-orange dye present in egg yolk is not even synthesized by the hen, but rather is ingested directly or at least in the form of a precursor along with its food. Figure 4. Carotinoids found in egg yolk. The sources of the characteristic color of an egg yolk are orange and red carotinoids (Fig. 4), typically mixed in along with the green mash the hens are fed. In the case of industrial egg production, carotinoids are added directly to standard mash. The effect is striking [6]: Figure 5 shows sections through 10 eggs, laid on successive days by the same hen after switching from a standard mash to one to which 20 mg/kg of carotinoids have been added. The color uptake, starting at the outer perimeter of the yolk, is clearly apparent with egg cells each of which has been allowed to mature for one day longer in the hen’s ovary. Figure 5.

Cross-sections through 10 eggs from the same hen, laid on successive days after switching from a normal mash to one containing 20 mg/kg of carotinoids. Figure 6 shows the effects of the reverse experiment: sections through 10 eggs laid on successive days by the same hen after switching from a mash supplemented with 20 mg/kg of carotinoids to one free of colorant. Figure 6. Cross-sections through 10 eggs from the same hen, laid on successive days after switching from a mash containing 20 mg/kg of carotinoids to one free of coloring agents. 0 < t < 3 h: Formation of the Egg White Shortly after the egg cell enters the oviduct, fertilization would become possible, unless it is prevented by the farmer, through a strict monastic separation of the sexes. Independent of whether fertilization occurs or not, every egg cell is converted within about 24 hours into a fully developed egg.

In the infundibulum, the funnel-shaped portion of the oviduct, egg albumen (egg white) is formed, along with its associated chalazae: a pair of spiral bands of protein within the egg white, twisted to the right, which extend out from the yolk at opposite ends of the egg and attach to the central viscous lining membrane of the egg white (Fig. 7). These provide a “shock absorber” effect for the suspended yolk. Additional layers of egg white are added within the second zone of the oviduct, the magnum. Figure 7. Schematic cross-section through a hen’s egg. The inner and outer shell membranes, which have a total weight of only 140 mg, are formed in the part of the oviduct known as the isthmus. Calcium carbonate deposition commences within the short tubular section of the uterus known as the shell gland, beginning on the wart-like end portions of the outer membrane fibers. The egg remains in the uterus “pocket” for a total of 20 hours, during which the rest of the shell forms — including the outer wall or cuticula. The albumen, or egg white, constitutes ca.

60 % of an egg’s weight, and is a 10 % solution of various proteins (for details see: " Proteins Present in Egg White "). A distinction is made between four concentric layers of differing viscosity. The innermost protein layer (vitellin membrane) forms a solid protein sleeve around the yolk, terminating at the spiral (protein) chalazae bands. Their fixation in a highly viscous albumen layer laid down later guarantees an elastic suspension of the yolk in the egg white. Outside of the vitellin membrane, and adjacent to it, are respectively three more albumen layers: One of low viscosity, one that is tougher, and then another with low viscosity. The differing viscosities of these layers is a function of the relative proportions of the roughly 40 dissolved proteins present. Overall, ovalbumin is the most prevalent (Fig. 8), representing ca. 60 % of the total protein content. It becomes denatured at the interface with air simply by vigorous beating, making it possible to prepare the stable whipped egg white that plays such a key role as the basis for meringues, soufflés, and angel food cake. Figure 8. Crystal structure of ovalbumin.

Among the other “egg-white proteins”, perhaps the most important is ovomucin, for its function in establishing the layer-like structure of egg white. A high content of ovomucin causes the corresponding egg-white layer to become highly viscous, developing gel-like properties, since the protein itself has a tendency to aggregate and form filamentous structures. 3 < t < 4 h: Formation of the Inner and Outer Shell Membranes The egg white is surrounded by two shell membranes, largely tightly bound together. The inner of the two has a thickness of 22 µm, the outer ca. 48 µm. Each consists of a closely woven network of protein filaments, acting together with the eggshell to protect the egg from penetration by bacteria. At the blunt end of the egg the two membranes separate, forming an air sac with a diameter of ca. 5 mm. 4 < t < 24 h: Formation of the Eggshell, Pigmentation, and the Cuticula Calcium carbonate crystals are deposited on the matrix created by the protein filaments of the outer shell membrane. If one were to implant a ping-pong ball in a hen’s uterus, no shell formation would occur.

On the other hand, were one to use a ping-pong ball to which outer shell membrane had been bonded, an “artificial” eggshell would form [10]. The contact between outer shell membrane and the innermost crystalline layer (Fig. 9) is made especially clear with the aid of images taken using a scanning electron microscope (Figs. 10–12). Figure 9. Eggshell structure. During eggshell formation [11, 12], the first step is application of a three-dimensional network of delicate protein filaments. Calcium carbonate in the form of calcite crystallizes on this matrix until the intervening space has been filled (Figs. 10 and 11). A second crystalline form of calcium carbonate, also found in nature, is aragonite, which is the basis of clamshells, pearls, and, for example, the shells of reptilian eggs. Figure 10. Calcium carbonate deposition commences on the wart-like mammillen of the outer shell membrane (view from within, 50-fold magnification). Figure 11.

Calcite is deposited on the network of fine protein filaments from the outer shell membrane (view from within, 500-fold magnification), and crystallizes upwards in columnar form on an organic matrix (palisade layer). Eggshell formation begins at the outer shell membrane with deposition of a mammillae layer ca. 70 µm thick, which transitions into the palisade layer. It is above this that the actual crystalline layer is to be found (Figs. 9–12). Figure 12. The outermost thin calcium carbonate layer is made of crystals oriented vertically, which are coated with a protein layer (cuticula) (external view, 50-fold magnification), such that the surface of the egg is smooth with a silky sheen. Pigments producing color are restricted to this uppermost calcium carbonate layer and the cuticula. An eggshell is permeated by 7,000–17,000 pores with a diameter of 10–60 µm (Fig. 13), which permit facile gas exchange with the surroundings, while at the same time serving as a barrier against penetration by dirt or microorganisms. Figure 13.

Pores at the shell surface (1500-fold magnification). Only the outermost regions of the calcium layers of the shell are pigmented. The actual amount and color of the pigment introduced is established genetically. Hens that lay white eggs are Mediterranean varieties, such as leghorns. Those producing brown eggs are of Asiatic strains, including Rhode Island reds. A few strains even lay bluish or greenish eggs (Fig. 14). Figure 14. Eggshell pigments. Araucanas (Fig. 15) and certain other strains incorporate blue biliverdin or its green zinc complex. The actual pigments are produced in shell glands, and dispensed by papillae lining the oviduct [13]. Figure 15. An araucana hen. Photo credit: Willowbrook Park . As suggested above, the amount, chemical composition, and distribution of pigments depends upon the strain of the hen, and the pigments themselves — protoporphyrin for brown and biliverdin-IX and its zinc complex for blue or green eggs — are synthesized in the shell glands [13,14].

Brown eggs are preferred by consumers — at least in some areas — who associate them with “natural, organic farming”. Actually, uniform brown pigmentation is simply a genetically derived attribute, since pigmentation serves in nature to protect the clutch of eggs, for which reason, the eggs of birds that lay their eggs on the ground are usually speckled [15,16]. In white eggs, pigment is almost entirely absent, but there is, in truth, absolutely no relationship between pigmentation and taste, style of flock management, or nurture of the laying hen. Eggshells are covered with the cuticula, a thin layer composed of proteins, polysaccharides, and lipids that contributes to the silky sheen associated with eggs. As far as the consumer is concerned, an eggshell amounts to nothing more than practical, disposable packaging. This of course fails to take account of the enormous effort on the part of the hen to prepare such an aesthetically pleasing object from marvelous composite materials.

In the process, the hen is required, for a single egg, to excrete 5 g of calcium carbonate; for a human that would correspond to 170 g (more than one-third of a pound) of the substance: and that every day! The inorganic chemistry involved in shell construction would appear to be trivial, since precipitation of calcium carbonate by simple exhalation through an aqueous solution of calcium hydroxide is one of the first examples of detection of an element one would encounter in a chemistry class. As simple as this reaction would seem for us, a hen would disagree mightily. Indeed, crystallizing such an enormous amount of calcium carbonate leaves her completely out of breath. How so? We need only to undertake a small calculation. The total CO2 reservoir in the body of a laying hen weighing 1.7 kg amounts to ca. 13 mMol. Producing a single egg shell requires 50 mMol. In other words, within a 24-hour period, her entire CO2 reservoir needs to be replaced almost three times. She is thus compelled to eat a great deal. The most problematic factor, however, is dealing with the resulting protons.

The daily diet provides a hen, through metabolism, with roughly 5 Mol of protons, but this is precisely balanced out through a corresponding utilization (homeostasis) [17]. Were the hen not to take compensatory measures, the pH of her body fluids would fall below 1 (!!), clearly a lethal value! The hen combats this threat of over-acidification through increased release of carbon dioxide, whereby the pH of the blood rises. This stimulated metabolism in a hen is actually quite apparent: when there is no egg in her uterus she breathes during the night while asleep only about seven times per minute, but more like twelve times per minute when an egg is present [18]. In other words, from the standpoint of the hen, creation of a shell is in no way simply a passive act of waiting, but rather a heavy piece of work. t = 24.2 h: The Laying Process The hen lays her egg with the blunt end first. An egg assumes its typical form while still in the oviduct (Figs. 3 and 4). It is, therefore, not a function of the laying process.

Topologically, an egg is a linearly deformed ellipsoid, an ovaloid, where the extent of the distortion is again a function of genetics. Irrespective of how round or deformed the hen’s egg, we will continue to follow its path to the breakfast table. In Part 2 we’ll watch the egg going from hen to a pot on the stove, whereas Part 3 is devoted to experimental reproduction of the chemical highpoints of cooking an egg. References [1] W. Ternes, L. Acker, S. Scholtyssek, Ei und Eiprodukte, Paul Parey Verlag, Berlin, Germany, 1994. ISBN: 9783860224045 [2] W. J. Stadelman et al., Egg Science and Technology, 4th ed., The Haworth Press, Binghamton, USA, 1995. ISBN: 9781560228554 [3] W. Ternes, Naturwissenschaftliche Grundlagen der Lebensmittelzubereitung, Behr's Verlag, Hamburg, Germany, 2008.

ISBN: 9783925673849 [4] G. Lück, P. Gaymann, Eiweisheiten: Experimente rund ums Ei, Herder Spektrum, Freiburg, Germany, 2005. ISBN: 9783451054952 [5] S. E. Solomon, Egg and Eggshell Quality, Manson Publishing, London, UK, 1997. ISBN: 9780723416470 [6] A. Hatzipanagiotou, W. Hartfiel, Arch. Geflügelkde. 1984, 48, 155. [10] G. Krampitz et al., Berl. Münch.Tierärztl. Wschr. 1973, 86, 313. Link [11] Y. Nys et al., Poultry Avian Biol. Rev. 1999, 10, 143. [12] I. Lavelin et al., Poultry Sci.

2000, 79, 1014. Link [13] R. Zhao et al., Poultry Sci. 2006, 85, 546. Link [14] J.-H. Fuhrhop et al., Liebigs. Ann. Chem. 1975, 1131. DOI: 10.1002/jlac.197519750612 [15] T. K. With, Biochem. J. 1974, 137, 596. Link [16] R. M. Kilner, Biol. Rev. 2006, 81, 383. DOI: 10.1017/S1464793106007044 [17] K. G. M. M. Alberti et al. The Hydrogen Ion in Normal Metabolism: A Review in Ciba Foundation Symposium 87 – Metabolic Acidosis (Eds: R. Porter, G.

Lawrenson), John Wiley & Sons, Chichester, UK 1982. DOI: 10.1002/9780470720691 [18] P. Mongin, World's Poultry Sci. J. 1968, 24, 200. DOI:10.1079/WPS19680021 Prof. Klaus Roth

Question: The vitelus is which part of an egg?
Answer: Yolk