One of the most general substitutes for meat is the egg. One would at first thought expect eggs to be of much the same composition as milk, since each funishes food for the growing animal, but when the different conditions are considered, the reason for the variation in this respect is readily seen. The egg must contain a large amount of nourishment in the most compact form. It must furnish all the materials necessary for growth, but it does not need to provide for activity to the extent that milk does. Consequently we find the carbohydrates wholly absent, and a much larger proportion of solid material than is present in milk. The solids are in the form of proteids, fourteen and eight-tenths per cent; fat, ten and a half per cent; and mineral salts, one per cent. This refers to the edible part only.
Diagram showing Composition of White and Yolk of an Egg.
The white of the egg contains twelve per cent of proteid, with practically no fat and a small amount of mineral matter, while the yolk has sixteen and two-tenths per cent of proteid and almost thirty-two per cent of fat.
The greater part of the mineral salts are also in the yolk, although the sulphur that causes the blackening of the silver spoon with which we eat our egg is chiefly in the white.
While eggs form a valuable meat substitute, it is difficult to use them wholly in the place of meat, since it takes so many eggs to equal a pound of meat. From eight to nine eggs constitute a pound. If the eggs have the composition given and meat contains eighteen per cent proteid, it would require about twelve eggs to furnish as much proteid as one pound of meat; and one who would have no difficulty in eating half a pound of beefsteak at a meal, would not wish to eat an equal weight of eggs.
Eggs like meat need to be supplemented by carbohydrate material. Bread and eggs furnish a satisfactory combination as well as bread and meat. Raw eggs are usually considered more easily digested than cooked eggs, although some experiments show that the cooked egg leaves the stomach in a shorter time than the uncooked. This is explained by the statement that the raw egg is digested largely in the intestine. Its failure to excite the secretion of gastric juice in the stomach makes it possible to use raw eggs in the diet when the stomach requires rest.
Hard cooked eggs take a longer time to digest than those lightly cooked, but from recent government experiments they seem to differ little in the completeness with which they are digested, an egg boiled three minutes having 8.3 per cent of its nitrogen undigested at the end of five hours; one boiled for five minutes having 3.9 per cent undigested, and one boiled for twenty minutes having 4.2 per cent remaining. Eggs cooked at 180 degrees Fahrenheit for five and ten minutes respectively were totally digested in five hours. Possibly the rapidity of the digestion of the hard cooked egg may depend on the fineness of mastication.
Whether eggs are to be used freely depends largely upon their price. Eggs at fifteen cents a dozen may be so used, while at fifty cents a dozen they can not be regarded as an economical source of food.