BACTERIUM TUBERCULOSIS 441 



BACTERIUM TUBERCULOSIS. 



Of the three pathogenic organisms liable to occur in the 

 sputum of a tuberculous subject, the tubercle bacillus gives 

 us the greatest difficulty in our efforts at cultivation. 



It is almost an obligate parasite, and finds c6nditions 

 entirely favorable to its development only in the animal 

 body. On ordinary artificial media the bacilli taken directly 

 from the animal body grow only very imperfectly, or, in 

 many cases, not at all. From this it seems probable that 

 there is a difference in the nature of individual tubercle 

 bacilli some appearing to be capable of growth in the 

 animal tissues only, while others are apparently possessed 

 of the power to lead a limited saprophytic existence. It 

 may be, therefore, that those bacilli which we obtain as 

 artificial cultures from the animal body are offsprings of 

 the more saprophytic varieties. At best, one never sees 

 with the tubercle bacillus a saprophytic condition in any 

 degree comparable to that possessed by many of the other 

 organisms with which we have to deal. 



For the cultivation of bacillus tuberculosis directly from 

 the tissues of the animal, the best method is that recom- 

 mended by Koch, viz., cultivation upon blood serum. Its 

 parastitic tendencies are so pronounced that even very 

 slight variations in the conditions under which one endeavors 

 to isolate bacillus tuberculosis from the tissues may cause 

 total failure. It is, therefore, necessary that the injunc- 

 tions for obtaining it in pure culture be carefully observed. 



Preparation of Cultures from Tissues. Under strict aseptic 

 precautions remove from the animal a diseased organ the 

 liver, spleen, or a lymphatic gland being preferable. Place 

 the tissue in a sterilized Petri dish, and dissect out with 



