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).