362 SUMMER. 



that are ardent sitters, she wears off great part of the 

 feathers on the under part, by friction in turning her 

 eggs. The increased heat which the breasts of female 

 birds have at that time, and the uneasiness produced 

 by that, which seem to be the great inducements to 

 sitting, no doubt help to remove the feathers. The in- 

 fluence of that action in the breast may be observed 

 in domestic birds ; pullets, for instance, will sit upon 

 the eggs of a duck, or upon stones, or upon the mere 

 earth, with all the attitudes of incubation, and perse- 

 vere in it for a considerable time, wearing off their 

 feathers by the friction, and probably also having the 

 juice of these partially absorbed by the heat. 



This heat of the breast appears to be as general a 

 phenomenon in the economy of birds, as the produc- 

 tion of milk in the mammalia ; and the removal of 

 the heat in the case of the bird, seems to be attended 

 with the same sort of pleasurable sensation as the re- 

 moval of the milk. In the case of domesticated birds, 

 we can partially, if not wholly, prevent this affection of 

 the female, by turning it to account in the production 

 of a greater number of eggs than would be deposited 

 for one brood in the natural state of the bird ; and the 

 same may be in so far accomplished with those wild 

 birds that do not easily desert their nests, by the same 

 means a constant removal of the eggs ; but that is no 

 argument against the universality of the affection. 

 Nor can we draw any more inference from those cases 

 in which we cannot prevail upon a bird to sit, than we 

 can from those in the mammalia, where a female some- 

 times cannot suckle. That is the reason why we, in 

 the absence of personal proof, have ventured to ques- 



