ARTIFICIAL HATCHING 131 



rately. The eggs must be fresh and of good quality, and 

 properly cared for, as previously described. The greatest 

 care must be given to the incubator from the time it is set 

 until the hatch is over. A successful hatch must come off 

 on time, starting on the twentieth day, and being completely 

 over by the end of the twenty-second. In short, a poor ther- 

 mometer, poor eggs and lack of attention are the three most 

 common causes of unsatisfactory hatches in an incubator. 



LABORATORY EXERCISES 



EXERCISE No. 20. Secure a small incubator. If one can 

 not be secured locally, some manufacturers are very willing 

 to donate small machines for classroom work. In the 

 presence of the class, the machine should be gone over 

 carefully and the form and use of every part explained. Later 

 the machine can be taken to pieces and the internal construc- 

 tion studied. Special attention should be devoted to the 

 perfection of construction, the means of temperature control, 

 method of ventilation, and the means of applying moisture. 

 A trip to a large hatching establishment, where mammoth 

 machines are operated, will make the study more interesting. 



EXERCISE No. 21. Place a small incubator in a cool, shady 

 corner of the schoolroom. Appoint certain members of the 

 class to care for it. The eggs can be brought by some of 

 the pupils. Follow carefully the instruction given in the text. 

 Each day a short period can be set aside, when those running 

 the machine can explain to the class the work done that day. 

 Each member should keep a little book with a complete 

 record of all operations and results, as specified in the text. 



EXERCISE No. 22. If two or more incubators are avail- 

 able, run them both at the same time. Operate both alike 

 in every respect, except in one machine place moisture, by 

 using sand trays, and in the other machine use no moisture 

 at all. Study the results as determined by the number and 

 weight of chicks hatched. 



