PRINCIPLES OF SWINE BREEDING 19 



This germ plasm is highly stal)le and independent of the 

 other cells of the body, which merely act as a carrier for 

 the germ plasm. 



Variations. — One of the fundamental principles under- 

 lying our progress in breeding is that no two animals are 

 alike. All are different. These differences are referred to 

 as variations. They constitute to a large extent our basis 

 of selection, and without selection we would have had no 

 improved breeds of swine. All variations are of two 

 types, the inherent or congenital ones, and those pro- 

 duced by environment. Only the inherited or congenital 

 variations that arise spontaneously from the germ plasm 

 are inheritable. Unfortunately, the breeder cannot al- 

 ways distinguish between the inherited and acquired 

 variations. Environment both magnifies and obscures 

 inherited variations, and thereby assists in the making 

 of selections. Variations arise spontaneously from the 

 germ plasm, or else they are produced environmentally. 

 As breeders, we are interested in both kinds of variations, 

 but primarily, of course, only in the congenital variations. 



Inheritance of acquired characters. — If a pig is stunted 

 and as a result develops a long snout and small stature, 

 we would call these acquired characters. If a pig has its 

 tail cut off, that would be an acquired character. For a 

 long time it was considered that all characters possessed 

 by an animal were inheritable and transmissible to the 

 next generation. In the light of more recent science we 

 must conclude that only those characters that are con- 

 genital and have their origin in the germ plasm are 

 inheritable. 



Mendelism. — This is something about which we have 

 heard much in the field of scientific breeding, yet as a 



