236 COMMERCIAL POULTRY RAISING 



the condition of the eggs. See chapter on selecting eggs for 

 incubation. If the eggs are in every way strong and hatchable, 

 the incubator will hatch them almost as well as the hen, and a 

 great deal more economically, because the machine can handle 

 such large quantities. 



The prospective purchaser of an incubator is sometimes per- 



Fig. 148. — Small single tray incubator suitable for the farmer and backyard 



enterprise. 



plexed as to which is the best type of machine for his purpose. 

 There are many different makes of incubators on the market, 

 which may be divided into two general classes: hot-air machines 

 and hot-water machines, all of which are constructed aJorig 

 moisture and non-moisture designs. In principle they are es- 

 sentially the same. The reason for this is clear: the whole 

 theory of incubation is based upon the fact that, if a fertile egg 



