The body's internal defense system is an extraordinarily complex and efficient mechanism. The lymphatic system is the key to the human body's immune response. Through the activation of the blood and lymphatic circulation system, many infections are successfully fought off before they gain hold in the body. Illustrates what happens when a man is infected with the common cold. Accessibility options on the DVD are: (1) audio description, (2) English subtitles, (3) English subtitles in a black box, (4) closed captions.