Sixty days after feeding with M. tuberculosis-inoculated soil, there was no statistically significant difference between negative control and challenged mice in regard to weight and macroscopic findings in the lungs, spleen, stomach and large intestine. Tissues collected from the negative control mice were free of granulomas. Furthermore, no granulomas were observed in the stomach and the intestine of five challenged mice, 0.38 granulomas mm22 lung were observed in one mouse, and 0.2 and 0.285 granulomas mm22 spleen in two other challenged mice (Fig. 4). The organs collected from the negative control mice remained sterile, in contrast to the challenged animals, which all grew M. tuberculosis, with bacterial loads of 120±100 c.f.u. ml21 in the lung, 0 in the spleen, 1760±1160 c.f.u. ml21 in the stomach and 140±100 c.f.u. ml21 in the intestine (Fig. 4).