330 FARM ANIMALS 



room where the surrounding temperature does not 

 vary greatly. The incubator should be started 

 running a few days before the eggs are to be placed 

 in it in order to determine whether the regulator 

 is running evenly or not. It is generally recommen- 

 ded that eggs should be turned twice daily after they 

 have been put in the incubator for about forty-eight 

 hours. Within from five to seven days the eggs 

 should be tested by taking out of the incubator and 

 holding before a light. Fertile eggs at this time 

 will show a dark spot surrounded by a net work of 

 veins while unfertile eggs will appear clear. They 

 should therefore be removed and may be used for 

 cooking purposes or for feeding to young chickens. 

 The temperature of the incubator should range 

 from one hundred and two to one hundred and 

 three F. and may be easily regulated by means of 

 a thermostat which is provided with all makes 

 of incubators. There is no point in making a 

 decision here between the different makes of incu- 

 bators. Nearly every one who has used them is 

 prejudiced in favor of the one with which he is 

 acquainted and the beginner will do best to look 

 into the matter in a practical way by consulting 

 with some one who has had experience with them. 

 The amount of ventilation required in incubators 

 is a matter about which some difference of opinion 

 prevails. It has been found by actual experience 

 that too much ventilation and too low a per cent, 

 of carbonic acid in the air of the incubator tends 

 to cause chickens to die before they are fully 

 developed. The action of carbonic acid consists 

 in softening or disolving the egg shells but does not 

 affect the egg membrane inside the shell. 



During incubation the eggs gradually decrease 

 in weight. During the first five days they lose 



