Recently there came under our observation a patient who had the obvious end-result of an extensive caseous-pneumonic tuberculosis1involving one entire lung. In spite of numerous coarse moist râles throughout that lung there was but slight expectoration. Examination of the sputum was repeatedly negative. Shortly after this incident another patient was seen who had a minimal lesion in the right apex. The pathologic condition was apparently productive in nature. Examination of the sputum was repeatedly negative. In spite of the negative sputum examinations, this patient suddenly developed a bronchogenic spread to the opposite lung. Not even at this time could tubercle bacilli be demonstrated in the sputum. Assuming in the first instance that the very nature of the pathologic condition made the presence of tubercle bacilli a foregone conclusion, and assuming in the second instance that the pathogenesis of the affair demanded free bacilli in the bronchial tree, we