This section is from the book "The Epicurean", by Charles Ranhofer. Also available from Amazon: The Epicurean, a Complete Treatise of Analytical and Practical Studies on the Culinary Art.
The eggs of chickens are most generally used. Boiled eggs should be moderately cooked; they are the most nourishing and easily digested; duck eggs are as nutritive as those of chickens. After these, the best are pheasant eggs, but they are very scarce. In order to discover whether an egg be fresh, hold it against the light of a caudle, and if transparent without being spotted then it is fresh.
The white of an egg consists of one part of albumen and one part solid matter, this appearing as an envelope to the albuminous liquid, and has the appearance of white flakes, also of a fatty substance formed of olein and stearine.
The yolk is composed partly of albumen, partly of a fatty matter containing olein, and another part that is colored, besides one of a solid membranous composition.