LOCAL OR GENERAL TUBERCULOSIS. 347 



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, 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 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, 1 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 be obtained and cultivated artificially, and these 



