MANAGEMENT OF INCUBATORS. 75 



should enlarge during incubation so that about the eighteenth 

 day* it occupies say on-s-fifth of the space unless it does, 

 the chick is too compressed to get out ; just as, if too dry, 

 the membrane may be too hard for it. Sometimes the 

 chick may be even deformed by the compression. This fact 

 will give the key to the probable cause of chicks being dead 

 in the shell, and to the owner's general management of 

 moisture. If the membrane be dry and leathery and the 

 air-cell large, more moisture is probably required in running ; 

 but if, on the contrary, the chick seems to fill the entire egg, 

 or nearly so, then too much moisture is the cause of failure, 

 and it must be reduced. There is another point (this is 

 chiefly established by Mr. James Rankin, long known in 

 America for his incubator work). In too moist an atmo- 

 sphere, rather too high a temperature, if it should also occur, 

 is four times as fatal. 



For more minute details the reader must be referred to 

 the directions with his own machine : but if these ignore 

 any of the above considerations, which have been well 

 weighed, he will do well to examine any persistent ill-luck 

 in the light of them. 



Eggs of water-fowl do best as a rule with about a degree 

 less temperature than hen-eggs, and rather more moisture 

 the last few days. It is also well to mention that ducklings 

 are often a day or two after pipping before they get out. 



The artificial rearing of chickens must be regarded as a 

 question entirely distinct from the artificial hatching of 

 them, and may often become advisable, or even necessary, 

 when they have been hatched under a hen. The mother 

 may die just when her care becomes most necessary ; or she 

 may be a valuable hen, whose eggs are much wanted, and 



* At any time after that the chicken may burst through the membrane 

 into the air-cell, and then appears to occupy more space. 



