William Clark's At War Within takes us on a fascinating tour through the immune system, examining the history of its discovery, the ways in which it protects us, and how it may bring its full force to bear at the wrong time or in the wrong place.Scientists have only gradually come to realize that this elegant defence system not only has the potential to help, as in the case of smallpox, but also the potential to do profound harm in health problems ranging from allergies to AIDS, and from organ transplants to cancer. Dr Clark discusses the myriad of medical problems involving the immune system, and systematically explains each one, making the complexities of this delicately balanced mechanism comprehensible to the lay reader.