348 BA CTERIOL OGY. 



cultures are capable of again producing the disease 

 when further inoculated. Thus the postulates for- 

 mulated by Koch, which are necessary to prove the 

 etiological role of an organism in the production of a 

 malady, are fulfilled. 



THE 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 conditions 

 entirely favorable to its development only in the ani- 

 mal body. On ordinary artificial media the bacilli 

 taken directly from the animal body grow only very im- 

 perfectly, 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 vari 

 eties. At best, one never sees with the tubercle bacillus 

 a saprophytic condition in any way 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 method by which one 

 obtains the best results is that recommended by Koch, 

 viz., cultivation upon blood-serum. Its parasitic ten- 

 dencies are so pronounced that even very slight variations 



