HOW TO CANDLE EGGS. 11 



As aging continues, the yolk may adhere slightly to the shell, but 

 a quick twist of the egg may set the yolk free without breaking it. 

 In such a case the egg is edible, but a very low grade. With further 

 aging the yolk will stick to the shell so that it can not be separated 

 without breaking the yolk sac, in which case the egg is classed as 

 bad. (See PL XI.) When the yolk is thus broken, as may happen 

 when the egg is turned quickly, the appearance of the egg before 

 the candle is the same as that of a mixed rot. Again, the yolk may 

 be adherent at one point and broken at another. These eggs de- 

 teriorate quickly into mixed or white rots. 



Dampness may be another factor causing the yolk to stick to the 

 shell. In this case molds penetrate the shells as far as the yolk, 

 which becomes very heavily attached to the shell, as shown in Plate 

 XII. 



The color of the yolk affects the color of the light passing through 

 the egg from the candle in much the same way as does the color of 

 the shell. For example, an egg with a light-yellow yolk will reflect 

 a pink-yellow light when held before the candle, and an egg with an 

 orange yolk a red light. Sometimes eggs with olive-colored yolks are 

 found. These reflect a green color from the yolk, which charac- 

 teristic has given them the name of "grass eggs." (See PI. V.) 

 The color of the yolk is not considered in the grading of eggs by the 

 candle, except in the case of " grass eggs," which are classed as 

 " seconds," because their color is abnormal. 



CHANGES IN THE YOLK DUE TO HATCHING. 



A few hours' incubation under the hen or exposure to warm tem- 

 peratures, as in summer, is sufficient to start the hatching of a fertile 

 egg. In its early stages this condition can be detected on candling 

 by the reddish glow of the area surrounding the germinal spot, which 

 in this stage of development is termed a " hatch spot." This is very 

 plainly seen when the egg is opened. A hatch-spot egg before the 

 candle and out of the shell is shown in Plate III. An egg in which 

 the hatching has progressed to this stage is considered edible but 

 is graded as a " second." 



Blood forms if incubation continues. At this stage in the devel- 

 opment of the embryo, the egg is considered inedible. A fertile egg 

 containing blood, due to hatching, is termed a " blood ring." Such 

 eggs are detected on candling by the circle, or portion of a circle, of 

 blood present around the reddish hatch spot area of the yolk. (See 

 PL VIII. ) If the embryo does not die, and conditions of incubation 

 are favorable, the different stages of development from the forming 

 of blood veins to the growing of the mature chick can be followed by 

 observation before the candle. After the embryo chick begins to 



