In important respects the specific allergy regularly induced in the tissues by an initial infection with tubercle bacilli is a peculiarly variable immunologic change. The intensity of the reaction to a standard dose of tuberculoprotein varies markedly in infected patients, and, apparently, after attaining a maximum development, the degree of sensitiveness to the material tends in general to diminish slowly as postcontamination years elapse. Furthermore, casual observation has indicated that the size of the average area of reaction to a standard dose of tuberculin is smaller in infected adults than in allergic children.
In order to investigate this last point, careful measurements were made for a series of adults and children of the fields of erythema of the Mantoux reactions to 0.02 mg. of old tuberculin1 and to 0.0001 mg. of purified protein derivative applied simultaneously in each instance on the right and left forearms, respectively. A modification of