EGGS AND THEIR VALUE AS FOOD. 11 



of egg whit© was found to consist of four bodies — ovalbmnen, con- 

 albumen, ovomucin, and ovomucoid. The ovalbmnen 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 young 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 especially 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- 



