720 
Journal of Agricultural Research 
Vol. XXIII, No. 9 
group was 1.07, one-half the specific gravity of the shell. The albumen, 
constituting approximately 10 per cent of the total egg volume, has a 
specific gravity of 1.31, which is not enough greater than that of the 
whole egg to have much influence should the protein content of the egg 
vary as much as one-half of 1 per cent, which is the maximum variation 
reported from analyses of a large number of eggs as reported by Willard 
and Shaw. 3 The fat, which constitutes approximately 12 per cent of 
the total volume of the egg, has a specific gravity of 0.881 (at ioo° C.). 4 
Slight variations in the fat content of the egg would not greatly influence 
the specific gravity, and the effect of an increased fat content would be a 
lower specific gravity. 
Variations in shell weight and thickness are therefore most likely to 
influence the specific gravity of the entire egg, since the specific gravity of 
the shell is nearly twice as great as that of the albumen and more than 
twice that of the fat in the egg. That the shell material has a most 
essential function in the nutrition of the embryo in the egg is known, 
for the chick at hatching time has five times as much calcium in its 
skeletal structure as is present in the egg contents. Harcourt and 
Fulmer s report (an average of 37 analysis) 0.03615 gm. of calcium oxid 
in egg contents, while the analysis of 65 chicks on file twentieth day of 
the hatch showed a calcium oxid content of 0.19487 gm. Normal egg¬ 
shells, however, contain at least 2.5 gm. of calcium oxid, so that even thin- 
shelled eggs contain enough calcium to satisfy all requirements, provided 
other factors influencing its assimilation are satisfactory. 
SUMMARY 
Our conclusions based on a close observation of 958 eggs and the sub¬ 
sequent growth of one lot of 150 chicks hatched are as follows: 
(1) There is little correlation between specific gravity, fertility, and 
hatchability of hens’ eggs. 
(2) The specific gravity of the egg has no relation to the viability 
of the chick hatched or to its growth rate the first five weeks after hatch¬ 
ing. 
(3) Variations in the thickness of the shell are more likely to influence 
the specific gravity of eggs than are variations in protein or fat content. 
•Willard, J. R., and Shaw, R. H. op. err. 
4 Spaeth, Eduard, der nachweis des eigelbes (eidotters) in mehlpabrikaten. In Eorsch.-Ber. 
iiber Eebensmittel [etc.], Jahrg. 3, Heft 2, p. 49-54. German abstract in Ztschr. Nahr.-Untersuch. [etc.], 
Jahrg. 10, no. 9, p. 171-173. English abstract in Analyst, v. 21, no. 246, p. 233-234. 1896. 
•Harcourt, R., and Eulmer, H. E. chemical work in connection with incubation problems. 
In Ontario Dept. Agr. Bui. 163, p. 57-66. 1908. 
