THE TUBERCLE BACILLUS. 299 



and with it the disease can be reproduced in suscepti- 

 ble animals, speaks for the accuracy of this assump- 

 tion. A conspicuous example of this condition is seen 

 in old scrofulous glands. These glands usually pre- 

 sent a slow process, are commonly caseous, and always 

 possess the property of producing the disease when 

 introduced into the tissues of susceptible animals, and 

 yet they are the most difficult of all tissues in which to 

 demonstrate microscopically 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 

 irr^ular, 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 dis- 

 ease 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 patho- 

 genic organisms liable to occur in the sputum of a tu- 



