METHODS OF HATCHING CHICKENS 317 



by means of a minimum thermometer in a glass bottle filled 

 with water. In 29 tests under five sitting hens the average 

 cooling temperature was 88.9 degrees. The lowest was 81 

 degrees. This represented the temperature of the interior 

 of the eggs after the hen had been oif the nest. Tests made 

 in incubators with the same instrument showed an average 

 of 94.3 degrees, with usual methods of cooling. The tests 

 were made in summer and the eggs were left out of the 

 machine about half an hour. 



An instrument of this kind may be used to advantage 

 by the incubator operator as a guide for cooling. 



Carbonic Acid Gas and Chick Development. The 

 hatching of the chick is a most marvelous thing. ,The shell 

 is the preserver of the egg. "Without it the egg could not 

 be kept wholesome more than a day or two. It also pro- 

 tects the germ of the chick from destruction. When it 

 comes to hatching, the shell is an obstacle. The chick be- 

 fore it can hatch and gain its liberty must devise some 

 means by which it can break down this prison wall. It 

 must grow a strong body, and it does it by making use of 

 its enemy, the shell. To break through the shell it must 

 put some of the shell into its body, otherwise it would not 

 be strong enough to hammer down the wall. 



How does it turn this enemy into an ally? By another 

 miracle, making use of another enemy a poison. A poison 

 that would kill the chick that is deadly to any living 

 animal the chick uses in obtaining nutriment and in break- 

 ing down its prison walls. A death-dealing poison under 

 the operation of this chicken chemistry is made to manu- 

 facture something that gives to the chick strength and a 

 right to live. Nature has decreed that fresh air is neces- 

 sary for the growing embryo, and while the shell protects 

 the contents and prevents the entrance of disease germs 

 and parasites, it admits air. As fresh air enters impure 



