THE INCUBATION OF THE EGG 191 



The egg chamber lies below the heating chamber and has 

 as its lower limit the bottom of the egg tray. It should be 

 roomy enough to render the handling of the trays easy. 

 The thermostat of the regulating device is located in the 

 egg chamber above the egg trays. 



The lowest division is known as the nursery, into which 

 the chicks drop as they come forward to the door after 

 hatching, attracted by the light. This relieves the conges- 

 tion in the egg tray during hatching. The bottom of the 

 nursery is usually supplied with a removable burlap tray 

 (Fig. 92). In the more pretentious machines it is replaced 

 by nursery drawers, which are a great convenience. 



A difficulty somewhat frequently encountered in nurseries 

 is that they are so deep and so far away from the source of 

 heat that newly hatched chicks dropping into them before 

 becoming well dried, are chilled. A difference in temperature 

 of 2° or 3° or even more may be noted for every inch 

 nearer or farther from the heat chamber that a thermometer 

 is placed. A thermometer lying on the tray of a nursery but 

 four inches deep will be found to register from 8° to 10° F. 

 lower than a thermometer whose bulb is on a level with the 

 eggs. A greater difference than this makes too severe and 

 sudden a change in temperature for the half-dry chick to 

 encounter, and cannot but do it injury. 



Types of Incubators. — Incubators are usually classified 

 according to the medium used in transmitting the heat from 

 "the heater to the egg chamber into "hot-air" and "hot- 

 water" machines. 



In actual efficiency there appeares to be no difference 

 between the two types. Hot-air machines are quicker 

 but not more accurately regulated. While the hot-water 

 type is less sensitive to outside changes of temperature, 

 once affected it is much slower in regaining the proper 

 temperature. 



Hot-air Incubators. — Hot-air incubators are divided 

 according to the method by which the air is used in trans- 

 mitting the heat into (1) diffusion, (2) radiation, (3) combi- 

 nation, and (4) contact types. 



With the diffusion types the heated air from the heater 



