THE INCUBATION OF THE EGG 209 



too much, it is probably best to adopt the common practice 

 of cooling the eggs." 



Moisture. — As the temperature maintained in the 

 incubator is determined by the temperature of the eggs 

 when incubated naturally, so the proper relative humidity 

 of the egg chamber would appear to be that which limits 

 the evaporation of the eggs to a normal rate. It should 

 be recognized, however, that even with natural incubation 

 the rate of evaporation will be different under different 

 conditions. Just what the optimum rate of evaporation or 

 the normal relative humidity is has not been definitely 

 determined. 



Normal Moisture Loss. — ^Atwood' computed, from obser- 

 vations made upon eggs incubated under hens, that the 

 normal loss of each of the first nineteen days for 100 eggs 

 that hatched was as follows: 



The difference in moisture loss between fertile and infertile 

 eggs is shown graphically in Fig. 106. 



Assuming that these eggs averaged two ounces each, the 

 loss for the nineteen days is 16.3 per cent. This work was 

 done in West Virginia. , 



Dryden^ found that in Utah, where the atmosphere is very 

 much less humid, the loss of weight in eggs under hens 

 was 14.87 per cent. 



Eycleshymer' found that the normal loss of an egg during 

 natural incubation was 13 per cent., but that healthy chicks 

 could be hatched when the evaporation was reduced to 

 9 per cent, by the introduction of moisture or increased 20 



' West Virginia BuIletinjNos. 73 and 98. 



2 Oregon Bulletin No. 100. ' Biological Bulletin, May, 1907. 



14 



