350 BEGINNINGS IN ANIMAL HUSBANDRY 



The fertile egg is one that will produce a chick under 

 proper conditions of what is called incubation. The infertile 

 or sterile egg cannot be hatched, and so has no value in repro- 

 duction, although for food it has equal value with the fertile 

 one. The fertility of the egg cannot be determined except 

 by incubation. After the egg has been under the hen for 

 five to seven days, ordinarily one may easily tell whether it is 

 fertile or infertile. If the latter, it will appear clear and show 

 none of the changes described in the following. 



The testing or candling of eggs is a simple process of 

 looking through the egg with the aid of special light. One 

 may take a piece of common cardboard, one side of which is 

 black, in which is cut an oval hole not quite as large as an 

 egg. If the cardboard is held before a lighted lamp in a 

 dark room, blackened side towards one, and an egg is held 

 in the hole, those that contain chicks will appear dark and 

 opaque except at the larger end, while sterile eggs will be 

 clear and show light. In the trade, where all eggs are 

 examined before a light, this process is known as candling. 

 Black lamp chimneys with holes in them are made for use in 

 a small way, but in the larger commercial trade, eggs are 

 candled over sets of lights arranged for this purpose. 



The incubation of the egg of the hen occupies a period 

 of 21 days. The following are some of the more important 

 changes that take place during incubation. During the 

 first twenty-four hours the germ enlarges to about a half inch 

 in size, within which the first stages of head and some other 

 parts appear. During the second day the heart begins to 

 beat and the blood to flow. By the end of the third day the 

 veins and arteries are considerably developed, and the young 

 chick turns on its left side. On the fourth day the wing 

 folds, and the folds forming the legs appear. The beak 

 begins to form on the eighth day, and shows its horny shape 



