Every particle of our body must bear an identification sign, or “tag”, saying ‘this is me’. If something does not have such a sign, or if the tag is foreign, tho particle would be saying: ‘this is not me’ Everything ‘other than me’ is destroyed by the immune system. I have compared two types of individuality spiritual and bodily to show tho all embracing significance of immunology, and the complexity and intricacy of the immune system. Only the future will reveal whether the mechanisms of the brain and the immune system are similar. This book has grown out of a booklet called Talks on New Immunology which was published in 1976 as a part of the “Eureka” series. The talks have been expanded in volume and their form revised in an effort to convey to the reader the huge volume of scientific information that has been accumulated by a young science of immunology.