Relating with our extensive serological studies on the antigen-antibody reaction in the system of M. tuberculosis in vitro, we have been engaged in experiments in vivo using the PCA test following after the Ovary's method. As the antigens, three tuberculin preparations i.e TA_2 (N 12.16%), PPD-s (N 13.6%) and PS (N 2.68%) were used. Rabbits' sera immunized with heat killed tubercle bacilli (Aoyama B strain) incorporated Drakeol-Arlacel emulsion as an adjuvant and patient's sera were used as the antibodies in the test. Rabbit immune sera were proved to be positive against all three tuberculin preparations in the PCA test. It is noteworthy that tuberculoprotein preparation such as TA_2 and even PPDs gave strong positively reactions. But, it is and unsolved problem that patients' sera have been proved to be negative in the similar tests.
