12 BULLETIN 471, U. S. DEPARTMENT OF AGRICULTURE. 



like bodies which are thought to maintain the equilibrium of nor- 

 mal nutrition and to stimulate growth. As yet there is not unanimity 

 of opinion as to the nature or the amount of these substances needed. 

 It seems certain, however, that they are rather widely distributed and 

 that a diet containing eggs, milk, fruits, and the other common foods 

 in wholesome variety is likely to supply a sufficiency. 



One of the constituents of egg albumin is sulphur, and the egg 

 albumin is readily decomposed with the liberation of hydrogen sul- 

 phid. The bad odor of rotten eggs is due largely to the presence of 

 this gas and phosphureted hydrogen, which is also formed. The shell 

 of the egg is porous, and microorganisms which cause the egg to rot, 

 or spoil, may gain access through the minute openings, and some of 

 these in their growth cause the formation of these sulphur com- 

 pounds. Even when a fresh egg is cooked, some sulphur is liberated, 

 as is proved hy the blackening of silver spoons or forks when they 

 come in contact with boiled eggs. It is a matter of common observa- 

 tion that when eggs are boiled the yolk where it joins the white 

 often has a more or less greenish color. Eubner has found that this 

 discoloration is due to the action of the hydrogen sulphid produced 

 by boiling on the iron of the vitellin of the egg yolk- in the presence 

 of alkali (formed when the white comes in contact with the yolk). 



In the table no figures are given for the composition of the egg- 

 shell, which, of course, is not used as food, though in times past it 

 has had some use in domestic medicine. The shells of hens' eggs are 

 made up very largely of mineral matter, containing 93.7 per cent cal- 

 cium carbonate, 1.3 per cent magnesium carbonate, 0.8 per cent cal- 

 cium phosphate, and 4.2 per cent organic matter. The shells of goose 

 eggs, on an average, have the following percentage composition: 

 Calcium carbonate, 95.3; magnesium carbonate, 0.7; calcium phos- 

 phate, 0.5 ; and organic matter, 3.5. The shells of ducks' eggs contain 

 94.4 per cent calcium carbonate, 0.5 per cent magnesium carbonate, 

 0.8 per cent calcium phosphate, and 4.3 per cent organic matter. The 

 shells of other eggs are doubtless of much the same composition. 



COOKING AND SERVING EGGS. 



Methods of serving eggs, alone or in combination with other food 

 materials, are very numerous. Those in which eggs are cooked 

 alone — for instance, boiling, frying, shirring, and poaching — are, in 

 general, simpler than those in which they are combined with other 

 materials. 



As regards the uses of eggs in cookery, they serve to improve the 

 flavor, color, and texture of such foods as cakes, while in such dishes 

 as custards and creams they also serve to thicken the material and to 

 give it the desired consistency. 



