Some of the cells of the body are active workers, manufacturing the secretions and fluids needed in the varied work of the system. Others belong to "the reserves," and are kept under "waiting orders" awaiting the call to duty in the case of an accident or other emergency. Some are stationary, others remain stationary until they are called into motion to meet some requirement, others are constantly moving about, some making regular trips and others being rovers. Some of the moving cells perform the work of carriers, some move from place to place doing odd jobs, others perform scavenger work, and a large number are employed on the police-force of the body, or else constitute the cell-army.

'Some enter the womb in order to have a body, as organic beings, others go into inorganic matter, according to their work and according to their...