To the Editor:— It is thought that several comments should be made relative to your editorial entitled "Prophylaxis of Spotted Fever," which appeared inThe Journal, May 20. By just glancing over the editorial it would seem that the observations of Anigstein, Bader, Young and Neubauer might have a clinical application as suggested. If one keeps in mind several known facts concerning Rocky Mountain spotted fever and the immunologic principles involved, it becomes evident that its practical application will be difficult if not impossible. In order for active immunity to develop following local infiltration with immune serum around the site of a tick attachment, that tick must not only be infected but actually have passed the rickettsias on to the patient. If these two prerequisites are not satisfied, certainly there will be no subsequent immunity. Since only one among several hundred ticks, at the most, is infected, and even