340 BACTERIOLOGY. 



eye, they are found in the granulation-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 demon- 

 strated microscopically. It is at the periphery of these 

 areas and in the progressing granular zone that they 

 are most frequently to be seen. 



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. As bacilli, they are difficult to 

 demonstrate here because the probabilities are that at 

 this stage of the process, owing to conditions unfavor- 

 able to their farther 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 visi- 

 ble. The facts that this tissue is infective, and that 

 with it the disease can be reproduced in susceptible 

 animals, speak for the accuracy of this assumption. 

 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, 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, 



