POULTRY KEEPING 



543 



vidual birds in the case of each breed. By careful selection of 

 breeding stock, therefore, it should be possible to control the color 

 of the eggshell to a great extent, so that it may be made to meet 

 any market demand. (Agr. Dep. F. B. 262.) 



Incubation. The history of incubation is rather obscure. Nat- 

 ural incubation, which is dependent upon the instinct of the mother 

 hen, seems to be conducted by the modern hen in just about the 

 same manner as that of the barnyard fowl of fifty or more years 

 ago. Artificial incubation, or hatching by machinery, is known to 

 be an old idea, and yet very little information upon original proc- 

 esses is to be found in our libraries. Eggs were hatched by arti- 

 ficial means centuries ago. Machines were invented and used suc- 

 cessfully for this purpose by the Egyptians long before the Christian 

 era. Very recently some of these hatching ovens have been found 

 by explorers. Some of them depended upon the customary fuel for 

 their supply of heat, while others relied upon stones heated in the 

 sun, and some, even, were found that obtained the necessary heat 

 from lamps. Besides the above sources of incubation heat, mention 

 can be made of decomposing animal and vegetable matter used 

 long ago with unknown success. Not many winters ago the writer 

 had the pleasure of forking out a live and healthy chicken from a 

 heap of compost near the door of his stable. Numerous other in- 

 stances of accidental incubation have been related, and man's in- 

 genuity has been exercised to devise machines and methods that 

 will insure the transition of the dormant egg into the living chick. 



The whole theory of incubation is based upon the fact that, if 

 a fertile egg is kept for a sufficient period of time under certain 

 conditions of heat, moisture, and position, it will be transformed 

 into a healthy fowl. 



The period of incubation varies with different species of fowls. 

 The average period of natural incubation is a little over twenty, or 

 about twenty-one days, for the egg of the common hen. This period 

 may be somewhat shortened or prolonged by variations in the con- 

 duct of the mother hen, and possibly by changes in the weather. 

 Should the woather be moderate and the hen quiet and faithful, we 

 need not be surprised if the eggs are all hatched by the close of the 

 twentieth or even the nineteenth day. Again, if the weather be 

 extreme or the hen restless and neglectful, we need not look for all 

 the eggs to hatch until the close of the twenty-first or the beginning 

 of the twenty-second day. The same applies to eggs from other 

 fo\vl>', except, of course, that each has its own period of incubation. 



Period of Incubation. 



