The story of menstruation begins, as the motherly narrator informs us, with the pituitary gland - a gland at the base of the brain that sends hormones throughout the bloodstream that order growth. When a girl reaches an age somewhere between 11 and 17 - the average is 13 - the pituitary gland sends maturing orders to the ovaries, which in turn order the uterus to create a thickened lining, filled with watery fluids and blood. If an egg is fertilized it will remain within that thickened lining for nourishment. But if the egg is not fertilized, the body has no use for the extra nourishment, and it passes out of the body - which is the process called menstruation. The narrator proceeds to disprove taboos against bathing or exercise during menstruation. She advises that girls should keep a calendar that keeps track of the number days between periods. And she notes how good posture, healthy foods and positive attitudes can affect the menstruation cycle.