BACTERIUM TUBERCULOSIS 411 



favorable to their development, and in the course of their 

 life-processes produce substances of a chemical nature 

 which serve to bring about characteristic changes in the 

 immediate neighborhood. In the beginning the fixed cells, 

 particularly the endothelial cells of the capillaries and 

 lymph-spaces, are stimulated to proliferation. With the 

 -onset of this phenomenon, evidence of other cell multipli- 

 cation may readily be detected in and about the affected 

 focus. As proliferation continues and as the local circulation 

 becomes more and more impaired, the centre of the diseased 

 area gradually assumes a condition of inactivity, and ulti- 

 mately presents all the characteristics of dead and dying 

 tissue. This death of tissue is one of the earliest, the most 

 easily recognized, and the most characteristic results of 

 tubercular infection, and may. usually be detected, in greater 

 or less degree, even in the youngest and most minute tuber- 

 cles. With the production of this progressive necrosis — for 

 progressive it is, as it proceeds as long as the bacilli live and 

 continue to produce their poisonous products — ^there is 

 in addition a reactive change in the surrounding tissues, 

 which results in the formation of a granulation-zone at the 

 outer margins of the dying and dead tissue. This zone 

 consists of small, round granulation-cells and of leukocytes, 

 all of which are seen in the meshes of the finer fibrous tissues 

 of the part. At the same time alterations are produced 

 in the walls of the vessels of the locality; these tend to 

 occlude them, and thus the process of tissue-death is favored 

 by a diminution of the amount of nutrition brought to them. 

 These changes may continue until eventually conglomerate 

 tubercles, widespread caseation, or cavity-formation results; 

 or from one cause or another the life-processes of the bacilli 

 may be checked and recovery occur. 



