276 BACTERIOLOGY. 



are commonly caseous, and always possess the property 

 of producing the disease when introduced into the tis- 

 sues of susceptible animals, and yet they are the most 

 difficult of all tissues in which to demonstrate micro- 

 scopically the presence of tubercle bacilli. 



In tubercles containing giant-cells the bacilli can 

 usually be demonstrated in the granular contents of 

 these cells. Frequently they will be found accumu- 

 lated at the pole of the cell opposite to that occupied 

 by the nuclei, as if there existed an antagonism between 

 the nuclei and the bacilli. In some of these cells, 

 however, the distribution 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, 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 again be obtained and cultivated artificially, and 

 these cultures are capable of again producing the 

 disease when further inoculated. Thus the postulates 

 formulated by Koch, which are necessary to prove the 

 etiological role of an organism in the production of a 

 malady, are all fulfilled. 



THE TUBERCLE BACILLUS. Of the three pathogenic 

 organisms liable to occur in the sputum of a tuberculous 

 subject, the tubercle bacillus will give us most 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 



