The body of a plant or animal is composed of small living bodies, most of them of microscopic size, called cells. These lead, to a certain extent, individual lives, and have individual characters, but they are built, as it were, together, like the bricks and stones of a house, to form the body. The cells are, all of them, nourished by the blood and lymph, and some are connected together by strands of connecting matter termed nerves. All the cells of the body are descendants from a single fertilised egg, which has resulted from the fusion of a paternal and maternal sexual cell. Among the cells of the body, and situated in special organs, are the sexual cells, likewise nourished by blood, but not connected by nerves with other parts of the body. _Reproductive Cells unaffected by Local Changes in the Body Cells._ Now there is no reason to suppose that these sexual cells residing in the bodies of the parent will be influenced by a change in the muscle or brain cells of the parent unless this change in some way or another influences the blood, the common go-between. But the blood is now known to be but a food and oxygen carrier, and an eliminator of used-up products. It is like a river laden with vessels carrying corn for the food of the big city, and nothing more. The life, the energy, the character of the body is the sum of the lives, the energies, and the characters of the cells--although these necessarily require the nourishment derived from healthy blood--just as the life of the city is the sum of the life of its citizens who require the nourishment of the corn. _Constitutional Change may, though it rarely does, affect the Reproductive Cell._