INCUBATION 



stated, does not depend upon external circumstances, nor 

 can it be influenced by them without damage or loss of 

 life ; for instance, no increase of heat beyond that employed 

 or generated by the parent birds will hasten or quicken 

 the production of the young bird, while, on the other hand, 

 a lower temperature is likely to prove fatal instead of 

 retarding its development. 



, The consideration of these immutable laws, and the con- 

 stancy of their appearance before us in such various 

 shapes and forms, prove beyond all doubt the existence of 

 phenomena of which we have at present but a faint 

 glimpse. Do we not see the same regularity of a fixed 

 time, and that the same number of days between the 

 changes that occur in the maladies to which we and other 

 animals are subject — are not the marked and noticeable 

 changes every seven days ? That this number, recurring 

 as it has and must have done in all time, doubtless led 

 our species to recognize the seventh day, and our laws, 

 terms of apprenticeship and imprisonment, leases of 

 houses and land, and endless other matters, probably came 

 into use from the observable regularity of this fixed and 

 unalterable law set before us. 



It is not only in the incubation of the eggs of birds that 

 this recurrence of the seventh as a period of change is con- 

 stant, but in the instance of birds' eggs it is so easily 

 watched and recorded, for the development of most 

 diseases is marked by the same time ; whether it be small- 

 pox, ague, or any other fever, the same law appears to 

 influence the state of the sufferer, and mark the changes 

 that take place regularly, for better or worse. 



Even in the ordinary course of the natural production 

 from the egg, we may be pardoned in remarking that much 

 misapprehension exists. It is by many believed that the 

 parent birds assist the young in breaking out of the egg. 



237 



