EGGS AND THEIR VALUE AS FOOD. 7 
yolk and two-thirds in the white. The most abundant nutrient is 
protein or nitrogenous matter, of which three-fifths of the total 
is present in the white and two-fifths in the yolk. Protein supplies 
nitrogen needed to build and repair the body tissue, and also some 
energy, being equal to carbohydrate in this respect, although inferior 
to fat, as noted on page 9. 
It is sometimes convenient to consider the relations of protein and 
energy in a definite amount of foodstuffs. In the case of a whole 
egg, 2.4 ounces of the edible portion would be required to supply 100 
calories of energy, of which the protein would contribute 36 calories. 
Of white, 6.9 ounces would be needed to supply 100 calories, and of 
this amount 97 calories would be contributed by protein. In case 
of the yolk, 1 ounce will supply 100 calories, of which protein con- 
tributes 17. 
Mineral matter is required by the body for building bone and other 
tissue and for regulating the body processes. In addition, recent 
research has shown that certain accessory substances (so-called vi- 
tamins, for example) are also present, which are required by the 
body in at least minute amounts. Since eggs contribute to all these 
body needs, their value as food is evident. 
In composition eggs resemble such animal foods as meat, milk, 
and cheese, more than such vegetable foods as flour and potatoes. 
As will be seen by the figures in the above table, hens' eggs and those 
of other poultry do not differ greatly in composition. Furthermore, 
there is practically no significant difference in composition between 
hens' eggs with dark shells and those with white shells, although 
there is a popular belief in some localities that the former are richer. 
Neither does the cooked egg vary materially in composition from the 
raw, though it varies markedly in texture. The yolk and the white, 
on the other hand, differ greatly in composition, the yolk containing 
considerable fat and ash, and the white being practically free from 
fat and containing somewhat less protein and ash and considerably 
more water than the yolk. Though both yolk and white, when raw, 
are fluid, they are not thought of as containing water any more than 
other familiar foods in which water is not visible as such but com- 
bined or mingled with the other constituents so that the whole food 
is more or less moist, liquid, or juicy. This and similar facts are 
brought out in figure 1, which shows in diagrammatic form the com- 
position of eggs and egg products. 
Though eggs are conceded to be a nutritious food, they are less 
concentrated, that is, they contain more water than some — cheese, 
for instance. On the other hand, they are more concentrated than 
many others, milk or oysters, for instance, and on the whole do not 
differ greatly in this respect from lean meat. Their general resem- 
blance in composition to other common animal foods suggests that 
