This program takes a look at the mechanics of the body’s internal defense system. The protected environment of the womb is contrasted with the pathogen-laden environment of the post-birth world. Passive immunity is distinguished from the body’s active lines of defense: the skin and its secretions, the inflammatory response, phagocytes, and lymphocytes. Case studies involving chicken pox, tetanus, and tuberculosis show different ways the human immune system seeks to protect the body from infection. And case studies involving asthma and HIV introduce the subjects of immune system hypersensitivity and failure. Contains nudity associated with childbirth. (20 minutes)