In a former publication (1) on this topic, it was stated that while the methods described in that publication provided preparations capable of successful diagnostic and therapeutic use, the problem was still under investigation. Most of the methods have been under constant study, and have been subjected to more or less important changes. The chief objects of the study were: First, to lessen the deterioration to which a number of the materials are subject; second, to effect a needed concentration of the active substances in some of the preparations; and, third, to simplify and facilitate the technical aspects of the methods. General Considerations. The various active substances responsible as exciting agents of atopic conditions are not all of the same nature. Studies carried out in this organization have shown that the atopens of pollens and of house dust and orris root are “non-protein” substances, whereas that of horse dander is at least in part a digestible protein.