4 ::*. Farmers' Bulletin 1167. 



easily influenced; by its food, how much more will the delicate little 

 creature, known as- the fetus'or' Embryo, be influenced by the character 

 of its food supply. A clear recognition of this fact will explain many 

 occurrences which are often attributed to supernatural influences, 

 and, at the same time, the breeder who recognizes this fact will not 

 neglect proper attention to the nourishment and care of the pregnant 

 mother as well as the nursing animal. 



Accidents and disease also are important in their effects on the 

 growing embryo. If an incubator is neglected on a cold night and 

 the eggs become chilled, the hatch is seriously impaired and a large 

 number of chicks are killed in the shell. If an in-foal mare is sub- 

 jected to very heavy strains or forced to pull extremely heavy loads, 

 the foal may be born too soon or even be killed in the womb. Con- 

 tagious abortion may get into the herd without the owner's knowing 

 it and cause the loss of a large proportion of calves. Heredity, how- 

 ever, has nothing whatever to do with any of these things. 



THE SCIENCE OF BREEDING. 



THE UNIT OF LIFE. 



The smallest unit of life is the cell. A single cell is very small, 

 usually of microscopic size. It is surrounded by a membrane, and 

 each cell usually contains a nucleus a sort of center of the things 

 that go on in the cell. The animal body contains millions of cells, 

 but those in which we are most interested at this moment are the 

 cells from the union of which a new animal life begins. They are 

 the germ cells. They contain the hereditary material which de- 

 termines the identity of each individual and which is known as the 

 germ plasm. This is the bit of life which passes down the line of 

 descent with each succeeding generation. It appears in the mother 

 in the egg cell, and in the father in the sperm cells. This material 

 is composed of elements which seem to be handed on unchanged 

 from generation to generation. Only a portion of the elements in 

 the germ plasm of the parent goes into each egg or sperm, however, 

 as is explained in more detail later. The element of chance enters to 

 such an extent in determining which elements shall go into a par- 

 ticular germ cell that there may be a marked dissimilarity among 

 individuals which are members of the same family. Even more im- 

 portant than the influence of food on the developing embryo and the 

 young, growing animal is the operation of chance in determining 

 the identity of the new life. 



The cells from which all life starts are developed in the genera- 

 tive organs. The egg (the female cell) is developed in the ovary 

 of the female; the sperm (the male cell) is developed in the testicle 

 of the male. In mammals each female has two ovaries, one on 



