210 BACTEBIOLOGY. 



are difficult to demonstrate here because the probabili- 

 ties are that in this locality, owing to conditions unfa- 

 vorable to their further growth, they are in the spore 

 stage, a stage in which it is as yet impossible, with our 

 present methods of staining, to render them visible. The 

 fact that this tissue is infective, and with it the disease 

 can be reproduced in susceptible animals, speaks for the 

 accuracy of this assumption. A conspicuous example 

 of this condition is seen in old scrofulous glands. These 

 glands present usually a slow process, are commonly 

 caseous, and always possess the property of producing 

 the disease when introduced into the tissues of suscepti- 

 ble 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 accumulated at the pole of the cell oppo- 

 site 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 

 tliese cultures are capable of again producing the dis- 

 ease when further inoculated. Thus the postulates 



