Rural School Leaflet. 657 



tester ; blackboard and color crayons ; and preferably also a chart show- 

 ing an enlarged, longitudinal section of the egg, with its various parts 

 in colors. 



An egg-tester can be made by placing a lamp ^^•ith chimney in a box 

 vrith a hole cut through the side slightly smaller than the egg. By 

 placing an egg over the opening in a darkened room, the interior of the 

 egg can be plainly seen. The same result can be accomplished with- 

 out an egg-tester by enveloping in the hands the egg in a darkened room 

 and looking through a small opening in the curtain at the sun. 



Any teacher who is unable to secure the above materials should take 

 such parts of the lesson as he can teach with the material that is avail- 

 able. We have tried to make the requirements very simple, but if 

 teachers cannot meet them, the greater part of the lesson can be given 

 without them. 



1. Strength of the egg shell. — Let each student hold a hard-shelled 

 egg between the clasped hands, the ends of the egg in the hollow of the 

 hand, and try to break it. 



Observe the great strength of the egg due to the arrangement of the 

 particles of the shell in an arch similar to the stones or bricks in the arch 

 of a bridge. 



This arrangement gives the egg great resistance against injury to the 

 shell, or to the chick which is developing within the egg. 



2. The coittciifs of an uncooked egg. — (a) Break a fresh, uncooked 

 egg in a saucer by separating the shell in the middle. 



Observe the "germinal disc," which appears as a light-colored spot 

 usually to be found on the upper surface of the yolk. 



The germinal disc contains the life principle of the egg. On the upper 

 surface it remains in close contact with the source of heat during natural 

 incubation, which is from above. 



(b) Note the "chalaza," or the whitish cords of denser albumen on 

 the sides of the yolk toward either end of the egg. These cords of denser 

 albumen serve to keep the yolk properly suspended within the albumen. 

 Thus the chick which develops on the upper surface of the yolk is pro- 

 tected from injury, if, through rough handling, it should come in contact 

 with the shell. 



(c) Note the transparent, watery appearance of the albumen (white 

 of the egg). 



The albumen supplies the food in liquid form by which the chick 

 grows within the shell. 



(d) Examine the shell and note the air-space usually found near 

 the large end. Observe the brittleness of the shell and the two tough 

 membranes best observed at the air-space, where the membranes separate. 



The air-space furnishes a readily available supply of fresh air to the 



