This little work gives a plain account of the facts and theories of immunity that will be welcome to the reader who comes to its perusal without any previous knowledge of the subject. A brief historical review is given and then the parts played by the body fluids, by the cells, and by the invading microorganism in the production of immunity are described and discussed. The rest of the book is divided into chapters dealing with the therapeutic uses and diagnostic applications of immunity reactions. Other chapters deal with anaphylaxis, the side-chain theory and chemotherapy, the latter including Wassermann's experiments in the destruction of malignant tumors. The explanations given are clear and the directions are practical. We have no doubt that this little manual will prove useful to many who have had difficulty in grasping what must be recognized as a somewhat difficult subject.