EGGS AND THEIR VALUE AS FOOD. 11 
of egg white was found to consist of four bodies — ovalbunien, con- 
albumen, ovomucin, and ovomucoid. The ovalbumen is the chief 
constituent and makes up the greater part of the egg white. The 
conalbumen has much the same chemical properties as ovalbumen. 
Ovomucin and ovomucoid are glycoproteids, and are present in small 
amounts. 
Egg yolk contains a number of different bodies, including about 
15 per cent vitellin (a protein) ; 20 per cent palmitin, stearin, and 
olein (in the fat) ; and 0.5 per cent coloring matter (see p. 4), be- 
sides some nuclein, etc., lecithin (a fat-like body containing phos- 
phorus and now regarded as one of the very important food consti- 
tuents, as it furnishes the body with phosphorus in a form in which 
it may be readily assimilated), and vitamins (see p. 7). Besides 
phosphorus, equivalent to a little over 1 per cent of phosphoric acid, 
the yolk contains such mineral elements as iron, calcium, and 
magnesium. 
Since in all cases the egg is designed to furnish the sole source of 
material for growth and development of the young individual for a 
considerable time, it is evident that it must contain all the elements 
required ; that is, it must be a complete food for the purpose intended, 
and this goes far to explain why it is such a valuable food for man. 
Milk is another familiar example of animal food containing all the 
elements of a complete food for the J 7 oung and growing individual, 
and milk and eggs are frequently, though inaccurately, spoken of as 
perfect foods on this account and have always been considered espe- 
cially important in the diet of invalids and children. It is true that 
they contain all the required elements for the growth and mainte- 
nance of the young mammal or the young bird, as the case may be, 
but this is not the sole test, for the elements are not in the right pro- 
portion for the sole nourishment of an adult individual. Man seems 
instinctively to have recognized this, since he uses eggs, as he does 
milk, in combination with other foods. 
Though rich in iron and calcium, eggs contain an excess of nitro- 
gen, phosphorus, and sulphur, and are, therefore, a predominantly 
acid food ; that is, in the process of digestion an excess of acid end 
products is formed which the well-being of the body requires should 
be neutralized with basic substances, best supplied by such foods as 
fruits, vegetables, etc. The nitrogenous material in eggs, as in milk, 
is readily assimilated. It is especialty noticeable that neither milk 
nor eggs contain purins, substances which are convertible into uric 
acid. In general, the iron, phosphorus, calcium, easily digested pro- 
tein, and fat in eggs make them rank high in the list of foods in a 
well-selected dietary. 
Many experiments have recently been reported concerning the pres- 
ence in eggs of such substances as the so-called vitamins and the lipoid- 
