GENERAL PRINCIPLES OF BREEDING. 27 



necessary to carry off the excess of carbon in the system. 

 But gradually, as man and other animals become natural- 

 ized in an elevated country, the digestive and respiratory 

 organs, and with these the capacity of the chest and abdo- 

 men, become suited to their new relations. Humboldt re- 

 marks on the extraordinary development of the chest in the 

 inhabitants of the Andes, producing even deformity; and he 

 justly observes that this is a consequence of the rarity of the 

 air, which demands an extension of the lungs. 



The effects have been referred to of use or exercise in 

 modifying certain parts of the animal form. The limbs of 

 many animate inured or compelled to speed become extended 

 in length, as of the dogs employed in the chase of the swifter 

 animals. The limbs of an animal deprived of the means of 

 motion become feeble and small, as the wings of domesti- 

 cated birds. In the natural state the cow has a small udder, 

 yet sufficient to contain the milk which her young requires; 

 in the domesticated state, by milking her, the organ be- 

 comes enlarged so as to contain a quantity of milk beyond 

 what the wants of her own offspring demand. Nor are the 

 characteristics thus acquired confined to the individuals on 

 which they have been impressed, but may be transmitted to 

 their posterity. 



The lessons taught by these illustrations 

 are obvious. None of our improved breeds are 

 adapted to all climates and all conditions of life. 

 To be at their best they must each be kept, as 

 nearly as possible, under the same conditions 

 of food and climate as those under which they 

 have attained their excellence. Any material 

 change in either of these conditions is liable 

 ultimately to make a material change in the 

 character of the breed. These changes are usu- 

 ally unfavorable ones, although not necessarily 

 so. Change of itself, when in the direction of 



