The Yolk. The yolk is anchored near the center of the egg by dense cordlike strands of white, called the chalazae, so that the yolk can revolve on its axis. The yolk in a fresh egg is round and upstanding. It is separated from the white by a membrane. As the egg deteriorates in quality, the yolk absorbs water from the white, swells, and tends to flatten. Finally a stage is reached at which the yolk breaks through the separating mem¬ brane and the two portions combine. On the surface of the yolk, a small light spot, called the "germ spot," may be seen. When an egg has been fertilized, the germ develops at this point. As the yolk swings in itsffiam- mock made by the chalazae, gravity holds the yolk so that the germ spot is always on top — a plan of nature whereby the germ spot is always nearest the body of the hen as she sits on her eggs. For the production of market eggs, the male birds are usually separated from the rest of the flock in order that infertile eggs may be produced. Infertile eggs keep better than fertile eggs. The color of the yolk varies from very pale yellow to deep orange, depending upon the food of the hen. The pigment of the yolk is chiefly xanthophyll, with carotene and cryptoxanthophyll present in small amounts. Hens fed in pens away from green food tend to produce eggs with light-colored yolks, while hens on range produce eggs with deep- yellow yolks. Alfalfa meal and large amounts of green food in the ration produce dark- colored yolks. Some feeds, such as cotton¬ seed, produce olive-green yolks. COMPOSITION AND NUTRITIVE VALUE Eggs vary considerably in composition ac¬ cording to the breed of the hen, the season, and feeding. The figures in Table XIX give the average proximate composition of eggs. The important points to remember about the composition of eggs are that (1) the yolk is approximately one third of the edible por¬ tion of the egg, and the white two thirds; (2) there is more total protein in an egg white than in a yolk, although the percentage is higher in the yolk; and (3) practically all the fat in the egg, 10.5 per cent, is in the yolk, which is about 32 per cent fat. Nutritive Value. Eggs are important as food because of their high nutritive value. Only the important nutrients contained in eggs are discussed here. Efficient Protein. Eggs are a good source of efficient protein, that is, protein of high biological value. The protein of the white is chiefly albumin, one of the complete proteins. The protein of the yolk is mainly ovovitellin, another high-quality protein. Egg proteins furnish all ten of the amino acids essential for building body protein. Energy. As a source of energy, eggs are not especially important. The edible part of the egg yields about 715 calories per pound, which means approximately 635 calories per pound as purchased (eight large eggs). This would be about 75 calories for each large egg or 70 calories for a medium-sized one. The [96] 1E. P. means "edible portion." energy value of the egg is due to the fat and protein content. There are no carbohydrates in eggs. Minerals. The iron content of egg yolk is high compared with most other foods. This iron is present in a form highly available to the body. Although the amount of iron in the white is low, the yolk is rich enough to make whole eggs an excellent source of this important blood-building mineral.

AI-modernized reading of the original text

The Yolk. The yolk is anchored near the center of the egg by dense cordlike strands of white, called the chalazae, so that the yolk can revolve on its axis. The yolk in a fresh egg is round and upstanding. It is separated from the white by a membrane. As the egg deteriorates in quality, the yolk absorbs water from the white, swells, and tends to flatten. Finally a stage is reached at which the yolk breaks through the separating mem¬ brane and the two portions combine. On the surface of the yolk, a small light spot, called the "germ spot," may be seen. When an egg has been fertilized, the germ develops at this point. As the yolk swings in its hammock made by the chalazae, gravity holds the yolk so that the germ spot is always on top — a plan of nature whereby the germ spot is always nearest the body of the hen as she sits on her eggs. For the production of market eggs, the male birds are usually separated from the rest of the flock in order that infertile eggs may be produced. Infertile eggs keep better than fertile eggs. The color of the yolk varies from very pale yellow to deep orange, depending upon the food of the hen. The pigment of the yolk is chiefly xanthophyll, with carotene and cryptoxanthophyll present in small amounts. Hens fed in pens away from green food tend to produce eggs with light-colored yolks, while hens on range produce eggs with deepyellow yolks. Alfalfa meal and large amounts of green food in the ration produce darkcolored yolks. Some feeds, such as cotton¬ seed, produce olive-green yolks. Eggs vary considerably in composition ac¬ cording to the breed of the hen, the season, and feeding. The figures in Table XIX give the average proximate composition of eggs. The important points to remember about the composition of eggs are that (1) the yolk is approximately one third of the edible por¬ tion of the egg, and the white two thirds; (2) there is more total protein in an egg white than in a yolk, although the percentage is higher in the yolk; and (3) practically all the fat in the egg, 10.5 per cent, is in the yolk, which is about 32 per cent fat. Nutritive Value. Eggs are important as food because of their high nutritive value. Only the important nutrients contained in eggs are discussed here. Efficient Protein. Eggs are a good source of efficient protein, that is, protein of high biological value. The protein of the white is chiefly albumin, one of the complete proteins. The protein of the yolk is mainly ovovitellin, another high-quality protein. Egg proteins furnish all ten of the amino acids essential for building body protein. Energy. As a source of energy, eggs are not especially important. The edible part of the egg yields about 715 calories per pound, which means approximately 635 calories per pound as purchased (eight large eggs). This would be about 75 calories for each large egg or 70 calories for a medium-sized one. The [96] 1E. P. means "edible portion." energy value of the egg is due to the fat and protein content. There are no carbohydrates in eggs. Minerals. The iron content of egg yolk is high compared with most other foods. This iron is present in a form highly available to the body. Although the amount of iron in the white is low, the yolk is rich enough to make whole eggs an excellent source of this important blood-building mineral.

Foods, their selection and preparation