THE BREEDING OF ANIMALS 



CHAPTER I 

 THE CELL 



THE greatest modern contribution to the science of 

 animal-breeding was the formulation of the so-called 

 cell theory. This fundamental biological generalization 

 ranks with the evolution theory in importance in many 

 respects; it has given a definite physical basis for in- 

 heritance. 



1. The cell theory. All the higher forms of life are 

 made up of cell units, and from these all parts of the 

 body are constructed. Although various in form, all 

 living cells are alike in having within a mass of proto- 

 plasm which Huxley called the " physical basis of life." 

 In the simple one-celled forms all functions are found in 

 the one cell, but in the more complex higher forms a 

 physiological division of labor results in the distribution 

 of functions among the cells. "It is to the cell," says 

 Verworn, 1 " that the study of every bodily function 

 sooner or later drives us. In the muscle cell lies the 

 problem of the heart beat and that of muscular con- 

 traction; in the gland cell reside the causes of secretion; 

 in the epithelial cell, in the white blood cell, lies the 

 problem of absorption of food, and the secrets of the 



1 Wilson, " The Cell," p. 6, 1911. 

 B 1 



