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 by 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. 
