Shows damage caused by disease and explains how the body combats toxins and disease-causing bacteria. Explains that the body’s own defence mechanism is the biggest obstacle to successful organ transplants. This is a lucid exposition of the manner in which the human body’s defences identify and reject intruders such as foreign proteins, bacteria or viruses. Animation and microphotography illustrate some of the known facts: the action of white blood cells and the response of the lymphatic system.