[The etiological agent of tuberculosis].

Author points out the reduced virulence of M. tuberculosis, that shows itself in a lower number of sputum smears and cultures positive for acid-fast bacilli and in a quick bacteriologic conversion of these cases. The most important test is again sputum smear with demonstration by microscope. No doubt that the use of antitubercular chemotherapy helped this paradoxical return to experimental methods employed by Koch, but on the other hand this use aided in forming some bacterial resistances. Author reminds that M. tuberculosis is supplied with particular characteristics, partly connected with its high lipidic contents. From this diversity as regards other bacteria rises also the difficult discovery of new efficacious antitubercular drugs.