Many kinds of eggs are eaten, but hens' eggs are the only ones necessary of consideration as a staple article of diet. The shell constitutes about 1.1 per cent. of the weight of the whole egg, the yolk 32 per cent., and the white 57 per cent.

Composition

Eggs are albuminous in nature and consist practically of the following substances - protein, water, fat and mineral matter. The composition of the hen's egg is as follows:

1 For further information, note "Eggs and Their Uses as Pood." Farmer's Bulletin No. 128, U. S. Dept. of Agriculture, Washington, D. C.

From this table it may be seen that the white of egg consists of eight-tenths water, the remaining portion being principally protein (albumin), with a little mineral matter, etc., the yolk is about half water, one-third fat, and nearly one-sixth protein, with almost twice as much mineral matter as the white.

Varieties

By eggs the product of the domestic fowl are commonly meant. The eggs of the duck, goose, turkey, etc., are edible, but are hardly suited for the sick, because of their stronger flavor. The purely white eggs are usually selected for the invalid, but many regard the brown-shelled egg as the more delicate.

Digestibility

Eggs are easily digested and very thoroughly absorbed in the intestines. If the absorption is delayed, decomposition follows with production of sulphuretted hydrogen and ammonia, which causes considerable gastro-enteric disturbance. The yolk is usually the cause of this disturbance. The digestibility of an egg depends upon its freshness and the manner in which it is cooked. 1Carelessness in cooking and serving may make an egg difficult of digestion and unappetizing, when, if it is cooked properly, it would be more palatable and easy of digestion. A raw egg, on account of its blandness, does not stimulate the flow of gastric juice and is not as easily digested as a soft-cooked egg; but by heating a raw egg the albumin is finely divided and is more quickly acted upon by gastric juice, consequently is digested about as quickly as a soft-cooked egg. Raw eggs are added to various foods, as milk and broth, etc., to give extra nutriment. Eggs are freely prescribed for those suffering from loss of flesh and strength, as the convalescent, anaemic, or in tuberculosis; in such cases as many as twelve eggs being given in as many hours.

1 See Albumin, p. 11.

A soft-cooked egg digests very quickly.

A medium-cooked egg is not as easily digested as either the raw, soft or hard-cooked, and should not be served cooked in this manner to the sick.

A hard-cooked egg as commonly cooked is difficult to digest, but cooked at proper temperature and chopped very fine will digest about as quickly as a soft-cooked egg.

Nutritive Value

Eggs are a very nutritious food, comparable with meat, milk, cheese, and other animal foods, both as regards total food material and the total protein and fat furnished by them. At twenty-five cents per dozen they are commonly considered very expensive, but this must not be interpreted too literally. Many persons will be satisfied with an egg who would not be with the equivalent food value in the form of meat, and eggs are valuable for giving variety to the diet and for furnishing an easily digested protein food, especially for the sedentary. For children they are much better than meat, because the fat is in an emulsified, and hence easily digested form, and because of their ash constituents. The yolk is rich in compounds of iron, phosphorus, calcium, magnesium. The protein of egg yolk is combined with lecithin, a phosphorized fat which has come to be regarded as an important constituent of food, especially for the growing animal. Egg yolks are frequently prescribed for invalids requiring an easily assimilated, concentrated food. It should be remembered that when fat is barred from the diet, egg yolk should not be given.

Egg white is valuable chiefly as a source of protein. Because of its mild flavor it can be combined with many substances, especially milk and other beverages (See "Albuminous Beverages," page 118), to increase the nutritive value of a liquid or semi-solid diet.

"With some persons, eggs induce constipation, or have a slight aphrodisiac effect. They contain sulphur, and unless digested before decomposition occurs in the alimentary tract, give rise to hydrogen sulphide gas. They should not be eaten by those suffering from flatulent dyspepsia, gastric dilatation, or any severe gastric derangement. They are contraindicated in acute Bright's disease.