Among 62 cases with excised lung the authors studied the morphology and stainability of tubercle bacilli found in 30 cavities proved to be acid fast bacillus positive by smears, 13 inspissated cavities, and 57 encapsulated caseous foci to the total of 100 foci; and obtained the following results. 1. Kuroda test is superior to Z.-N. test for the detection of tubercle bacilli, and it is also better for determining the changes in acid resistance of the bacilli. A.-F.-G. test and Z.-H. test surpass Z.-N. test and Kuroda test in the rate of bacillus detection as well as in the rate of determining granulation paterns. 2. In Z.-N. test the acid resistance of bacilli coincides relatively well with the growth rate, showing a negative tendency in the growth rate along with the decrease in the acid resistance; whereas in A.-F.-G. test along with the improvement of focus a decrease in the number of acid fast type of bacilli, showing an accompanying increase of the growth (-) tendency. On the other hand, in Z.-H. test the changes in the stainable type bacilli do not necessarily coincide with the nature of focus and growth rate. Moreover, the acid resistance roughly parallels with the deformation of bacilli, and along with a decrease in the acid resistance an increase in the deformation of bacilli can be recognized, especially a granulation tendency becomes marked. 3. According to the kinds of foci, bacilli in the tuberculous cavity are greated in number and the growth (positive) rate is highest, showing an increasing tendency of long bacilli, while in the inspissated cavity the long bacilli are decreased in number and short bacilli show an increasing tendency; and in the encapsulated caseous focus the granulation tendency becomes marked. Namely, with the improvement in foci bacilli tend to decrease, showing a concurrent decrease in the growth rate(-), and moreover, with the healing of foci an increasing tendecy of short bacilli as well as the fibrilllation and granulation tendencies of bacilli can be recognized. 4. In the case where bacilli are being expelled by chemotherapy of the focus, the greater the amount of antituberculous agent used, the greater is the increase in the growth rate (positive), showing a marked increasing tendency in the number of long bacilli as well as a higher acid resistance by the A.-F.-G. test. In the cavity where there occurs no expulsion of bacilli, the greater the amount of therapeutic agent used, the greater is the increasing tendency of the growth rate(-) as well as the number of short bacilli. Further more, on the whole the granulation tendency grows more marked as the amount of chemot herapeutic agent is increased. There is no correlation between the concurrent use of INH, collapse treatment of the lung, and bacillus shape. Likewise no relationship can be recognized between the duration from the onset of disease to operation, culture results, the shape and stainability of bacilli. There can berecognized on the whole no correlation between the resistance against drug and the length of bacilli, and in the case of acid fast bacilli the change in the shape of bacilli is somewhat less and the acid resistance is relatively well maintained. In the case of stainability (positive) and cnlture (-) bacilli, the decrease in the resistance and shortening deformation and granulation tendency are marked.