414 APPLICATION OF METHODS OF BACTERIOLOGY 



when the process has advanced to a stage easily recognizable 

 by the naked eye, they are distributed through the granula- 

 tion-zones in clumps and scattered about in large numbers. 



In the central necrotic masses, which consist of cell- 

 detritus, it is rare that the organisms can be demonstrated 

 microscopically. It is at the periphery of these areas and 

 in the progressing granular zone that they are to be seen 

 most frequently. 



This apparent absence of the bacilli from the central 

 necrotic area and often from old caseous tissues must not 

 be taken, however, as evidence that these materials are not 

 infective, for with them the disease can be reproduced in 

 susceptible animals by inoculation. A conspicuous example 

 of this condition is seen in old scrofulous glands. These 

 glands usually present a slow process, are commonly caseous, 

 and always possess the property of producing the disease 

 when introduced into the tissues of susceptible animals, 

 but 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 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 and are 

 always capable of reproducing the disease when introduced 



