This modest book is a most commendable and systematic presentation and discussion of the basic factors of immunity and resistance. The author has kept consistently to fundamentals and has analyzed them in clear terms. This is the first concise analysis of the work that has been done on the basis of the present knowledge of the chemical specificity of the fundamental factors of the immunologic Trinity—the antigen, the binding substance and the substrate. The evidence is reviewed that proves "that serologic properties are intimately connected with chemical constitution." The bibliography of the basic research and the index make this small book a necessary and useful reference tool for workers in the field of immunology.