72 POULTRY BREEDING IN 



and the air contained in the egg is condensed, thus leav- 

 ing a vacuum. Now, as the shell is porous, and the pres- 

 sure of the outer air much greater, it forces itself gradually 

 through the pores of the shell until the equilibrium is 

 reestablished, thus forming the depression of the fluid 

 part observable in old eggs at the round end ; and as the 

 contact of the air with the fluid part very soon alters the 

 taste, and renders them unfit for hatching from, it becomes 

 essential that the eggs should be preserved as early as con- 

 venient after being laid. 



2. Why should eggs be preserved better in rarefied 

 air than by merely packing them in air-tight jars? 



The variations in the temperature of the atmosphere 

 from below freezing point to summer heat are important 

 considerations in preserving eggs. The elasticity and 

 expansive properties of air need not be explained here, as 

 they will require a full explanation under the questions in 

 reference to regulating heat. I will, therefore, only say, 

 that if an air-tight jar were closed up during cold weather 

 without the air within being first rarefied, it would, pro- 

 vided it remained air-tight, stand a good chance of burst- 

 ing during the summer heat, which would expand the air 

 in the jar, and the pressure on the eggs would be so great 

 that a quantity of air would be forced on the fluid through 

 the pores of the shell. Were it possible to preserve the 

 eggs immediately on being laid at the temperature of 

 blood-heat, and during the hottest summer days, the jars 

 would not require rarefying ; but as such conditions are 

 almost impossible to command, as the eggs must unavoid- 

 ably on cooling absorb a certain amount of air, and as 

 the atmosphere might become still warmer than on the 



