Rabbits sensitized with the human tubercle bacilli were reinfected with the same bacilli intravenously and were treated with PAS or INAH. The lungs were histologically examined at certain intervals using routine procedures. 1) In the lungs of the animals treated with PAS, miliary tubercles were found in the third to the 7th day after the inoculation, being similar to those in the lungs of the reinfected and non-treated animals. The tuberculous changes developed intensively with propagation of the bacilli for 2 weeks after the inoculation, while thereafter the healing processes as indicated by proliferation of connective tissues and collagenization of argyrophilic fibers, began to appear more rapidly than those in control animals. 2) In the animals treated with INAH, prominent hyperemia and bleeding were observed around the tubercles in the lungs on the 3rd day after the infection. For 2 weeks the tuberculous lesions were similar to those found in the lungs of PAS-treated animals in their severity. Thereafter the lesions began to reduce their severity with increased proliferation of blood capillaries, hyperemia and bleeding
