BACTERIUM TUBERCULOSIS. 357 



however, the distributiop of the bacilli is seen to be 

 irregular, and they will be found scattered among the 

 nuclei as well as in the necrotic centre of the cell. As 

 the number of bacilli in the giant-cell increases the cell 

 itself is ultimately destroyed. 



Tubercular tissues always contain the bacilli or their 

 spores, 1 and are always capable of reproducing the dis- 

 ease when introduced into the body of a susceptible 

 animal. From the tissues of this animal the bacilli 

 may be obtained and cultivated artificially, and these 

 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, in the strict sense of the word, a parasite, and 

 finds conditions 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 tis- 

 sues 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 arti- 

 1 The property of spore-formation is assumed, not proved. 



