1394 The Cornell Reading-Courses 



torily by rolling them around on the tray with the flat of the hands. They 

 must not be shoved roughly against one another nor rolled harshly. The 

 tray may be turned end for end at each turning of the eggs; and if two 

 trays are used they may be interchanged at one turning and turned end 

 for end the next time. 



Cooling. — The successful cooling of eggs during incubation counter- 

 balances, to some extent, the still imperfect methods of ventilation. To 

 cool eggs properly, one must consider the length of time they have been 

 incubated, the weather conditions, and the room temperature. It is not 

 known just how much cooling is necessary for the best results, nor can a 

 time-table be made that will work successfully with all types of incubators 

 and under the varying atmospheric conditions. But the fact that eggs 

 incubated by hens undergo more or less cooling and hatch well, makes it 

 appear essential that those artificially incubated be treated correspond- 

 ingly. Results prove this theory to be true. 



It has been shown that excessive ventilation causes a too rapid evapora- 

 tion of the egg contents. Eggs cooled too much are affected similarly. 

 Therefore, for the first seven days it is best not to leave them out of the 

 machine longer than is necessary for proper turning. The length of time 

 to cool may be determined by touching several eggs to the eye or the lips. 

 If sufficiently cooled, the eggs will feel cool at first touch. They should 

 never be left out long enough to become cold. Some authorities assert 

 that it is possible to govern the amount of cooling, to a certain extent, 

 by comparing the size of the air cells with those undergoing the natural 

 process of incubation, notwithstanding the fact that the air cells of different 

 eggs in the same machine will vary in size. If the general tendency of 

 the incubator eggs is to have larger air cells than those under hens, less 

 cooling is necessary, and vice versa. This method, however, is fast becoming 

 unpopular. By observing the air cells of eggs being incubated in various 

 machines at this Station, each operated by a different person, it has been 

 found that eggs in moisture machines usually have smaller air cells than 

 those in non-moisture machines. This fact does not appear to have any 

 material influence on their hatching power, as there was no great difference 

 in the percentage of chickens hatched. The above instance is verified by 

 extended observations and experience with many incubators operated at 

 one time under practically ideal conditions. Little dependence should 

 be placed on the relation of the size of the air cells to cooling. It is highly 

 probable, however, that cooling, ventilation, and moisture have some 

 influence on the size of air cells. 



When cooling is begun it will take only a very few minutes, perhaps 

 four or five, to cool the eggs sufficiently, the length of time depending on 

 the temperature of the room. The cooling should be gradually extended 



