Great as is the physical difference between a fully cooked and an uncooked egg, it is no less remarkable in the degree of digestibility conferred upon it by the process. Uncooked, it passes by the most simple processes of assimilation from the digestive to the nutritive and circulatory organs, and is at once employed in nourishing or sustaining the bodily functions. Unduly cooked, the egg resists the action of the gastric juices for a long time, and becomes unsuited to the stomachs of the weak and dyspeptic. A raw or soft-boiled egg is of all varieties of food the most nourishing and concentrated; a hard-boiled egg is apt to trouble the digestion of the strong and healthful, and its nutrient properties are sensibly impaired. The yolk contains water and albumen, but associated with these is quite a large number of mineral and other substances which render it very complex in composition. The bright yellow color is due to a peculiar fat or oil, which is capable of reflecting the yellow rays of light, and this oil holds the sulphur and phosphorous which abound in the egg. If the yolk be removed and dried, and the yellow oil separated, it will be found to form two-thirds of the substance. The whole weight in its natural state is about three hundred grains, of which three-fifths is water; of the white more than three quarters is water. The yolk and albumen of a fecundated egg remains as sweet and free from corruption during the whole time of incubation as it is in new-laid eggs, and there is but little loss of water; whereas an unfecundated egg passes rapidly into putrefactive decay and perishes. Any one who eats three or four eggs at breakfast consumes that number of embryo chicks. All the materials which enter into the legs, bones, feathers, bill, etc., of the new-born chick, exist in the egg, as nothing is derived from outside. The little creature which has just pecked its way out of its calcareous prison-house, has lime and phosphorus in his bones, sulphur in his feathers, iron, potash, soda and magnesia in his blood, all of which mineral constituents come from the egg, and are taken into the stomach when it is eaten as food. The valuable or important salts are contained in the yolk, and hence this portion of the egg is the most useful in some forms of disease. A weakly person, in whom nerve force is deficient and the blood impoverished, may take the yolks of eggs with advantage. The iron phosphoric compounds are in a condition to be readily assimilated, and although homoeopathic in quantity, nevertheless exert a marked influence upon the system. The yolks of eggs, containing as they do less albumen, are not so injuriously affected by heat as the white, and a hard-boiled yolk may be usually eaten by invalids without inconvenience. The composition of a fresh egg, exclusive of the shell, may be presented as follows: