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The Cornell Reading-Courses 



moved by turning the egg about. Occasionally the germ will, be hardly 

 visible, but its presence is readily detected by a darker appearance of the 

 egg contents than is shown by an infertile egg. If for any reason the per- 

 son doing the testing is in doubt as to whether a germ is alive or dead, it 

 is well to mark the egg and test it later ; this practice will help to make the 

 operator more expert and will add interest to the work. 



An infertile egg looks like a fresh egg, the only apparent difference 

 being in the size of the air cell. In Fig. 35 may be seen several types of 

 eggs arid conditions of development as they appear after seven days of 

 incubation. Dead germs are found in various forms and sizes on the 



Fig. 34. — A convenient arrangement for sunlight testing: i, Tray for vnfesled eggs; 2, 

 tray for good eggs; j and 4, trays for infertile and dead germ eggs; 5, curtain in place 



seventh day, the most common of which are shown in Fig. 36 (2, 3, 4, 5, and 

 6). All of these should be discarded. Blood rings, also shown in Fig. 36, 

 are caused by the bursting of the blood vessels, due to overheating or \fi 

 an otherwise weakened condition. 



The second test is more difiiciilt to make than -is the first. Many of the 

 weaker germs will not differ materially in appearance from those that are 

 dead, and some that have died within a few days of the test cannot be 

 distinguished from the living embryos. However, if an egg contains a 

 strong germ it will be dark and apparently fairly well developed ; the space 

 below the membrane forming the air cell will be filled, making the division 

 dark and firm, and occasionally life will be denoted by motion within the 

 egg. The less developed the embryo appears to be, the fewer are the 



