Soon after the introduction of the cutaneous test of Pirquet and the intracutaneous test of Mantoux, it was noticed that persons varied greatly in skin sensitiveness to tuberculin, the active principle of which has been recently proved by Seibert1 to be a true protein. Various reasons have been ascribed for this difference in the grade of skin reaction. It was at first naturally believed to be related to the degree of tuberculous activity, or to the amount of tuberculotoxins made by the living tubercle. Later, persons were noted to be hypersensitive to tuberculin in whom no active tuberculous processes could be demonstrated. Krause2 and Willis3 have both submitted experimental evidence that the degree of sensitization is related to the time of infection, and that it is increased by reinfection.
It is not my intention to discuss in detail the nature of the tuberculin reactions. In view of