MANAGEMENT OF INCUBATORS. 73 



the sliding weight, or turn of a screw, is needed to alter about 

 one degree. Again, as the chick grows, it adds real animal 

 heat to the chamber, which will have to be compensated, 

 and must always be watched against. If it be found that 

 eggs habitually hatch late, a degree higher should be tried ; 

 if habitually early, the converse. This is the only safe rule, 

 because the precise position of thermometer, or other points, 

 may affect the apparent temperature at which an incubator 

 works best. 



5. For these reasons it does not answer to be putting in 

 fresh eggs during a hatch. The chill to the others can be 

 avoided by heating up the new ones first ; but in any case 

 they upset the regulation, lacking the animal heat of the 

 others. It is, however, very important to " test " the eggs 

 and withdraw sterile ones ; and still more so to withdraw 

 any addled or decomposing eggs. 



6. The eggs should be carefully turned twice a day to 

 prevent the germ adhering to one side, as it does in many 

 cases if left in one position. At the morning turning, the 

 eggs may be aired or cooled for five to ten minutes in warm 

 weather, provided the incubator can be kept closed and 

 warm whilst this is done. In cold weather they are better 

 put back again as soon as turned, if by hand. Where the 

 eggs are turned mechanically, however, five minutes may be 

 allowed, which refreshes the air in the air-cell. It is now 

 known that airing has been much overdone. 



7. So also has ventilation, which is most injurious if 

 causing any draught over the eggs. They need very little 

 ventilation during the first week or ten days then gradually 

 more. In heavy sultry weather, when a fire will hardly 

 burn, hatching will be greatly promoted by making a breeze 

 about the incubator occasionally, fanning the air with a 

 piece of thin board. 



8. Another point which has been much over-pressed is 



