HATCHING THE EGGS. 31 



although they will hatch when much older if carefully 

 preserved under woolen covers, and turned daily. 

 The trays should be crowded at first, since, on testing 

 the eggs on the fifth day, many may be found infertile 

 and will have to be taken out. 



After an incubator full of eggs has once been 

 started, no additional eggs should be put in until the 

 hatching is completed. This may be accepted as a 

 rule to tie to without giving all the reasons for it here. 



Eggs to hatch well must lose a part of the water 

 contained in them. This loss occurs by evaporation 

 through the pores of the egg-shell. Under the hen 

 evaporation is checked just at the right time by a 

 slight film of oil from the hen's body that shows itself 

 in the gloss that appears on eggs that have been in 

 the nest for a few days. In the incubator the evapor- 

 ation will continue for the whole period of incubation 

 and be excessive unless checked by supplying a moist 

 atmosphere to the egg trays. Each manufacturer has 

 his own method for furnishing the required moisture, 

 or retaining it by proper ventilation. There is enough 

 moisture in an egg to hatch it, but improper ventilation 

 will drive it out. 



A reliable thermometer is one of the first essen- 

 tials to success in artificial hatching. The secret of 

 many failures may be traced to thermometers with 

 scales inaccurately marked between the points 100 

 degrees and 105 degrees, just where accuracy is 

 especially required in hatching eggs. 



The proper temperature for hatching is considered 

 to be 102 degrees to 103 degrees. This is the tempera- 

 ture, not of the egg chamber, but the temperature of 



