TESTING 



343 



keep the wick of a wet-and-dry-bulb hygrometer in good condition 

 in the incubator, because the high temperature will quickly dry 

 it out and make frequent changes of the wick necessary. For 

 practical purposes, the spiral or horse-hair hygrometer is much 

 more satisfactory. To the inexperienced operator, however, the 

 increasing size of the air cell will be the safest guide. 



Testing. To determine the fertility of the eggs, as well as to 

 study the developing embryos and thus ascertain whether the 

 machine is running properly, it is advisable to test or candle the eggs 

 once or, better, twice during 

 the hatch, preferably on the 

 seventh and fourteenth days. 

 The egg tray should be re- 

 moved to a dark testing room, 

 and the light for testing pro- 

 vided either by a kerosene lamp 

 or an acetylene or electric light 

 placed in a small tight box 

 with circular opening about 

 one inch in diameter. Electric 

 light is the best, the light from 

 a kerosene lamp not being 

 powerful enough to penetrate 

 the shell of the egg (Fig. 161). 



The egg tray should be 

 placed on the right-hand side 

 of the lamp box, the person 

 standing in front, with a du- 

 plicate empty tray at his left 

 hand in which to put the eggs 



as tested. The testing lamp should be so placed that the open- 

 ing is about six inches above the waist line and one foot in 

 front of the operator. The untested eggs should be taken two 

 or three at a time from the full tray, and transferred one at a 

 time to the other hand, grasping them between the thumb and 

 forefinger with the large or air cell end outward. As the eggs are 

 moved, they are brought one at a time in front of the opening, 

 and given a gentle rotary motion. This will move the contents, and 

 the light penetrating the shell will reveal the presence or absence 

 of the germ, and its condition. The chief points to be determined 

 in the seventh day's test are the size and location of the air cell, 



FIG. 161. A useful, home-made egg tester. 

 Electric light is used. Two holes allow the 

 testing of two eggs at once. 



