LOCAL OR GENERAL TUBERCULOSIS 337 



phenomenon karyokinesis, evidence of cell multiplica- 

 tion may readily be detected in and about the affected 

 focus. As proliferation continues and as the local cir- 

 culation becomes more and more imjjaired, the centre of 

 the diseased area gradually assumes a condition of in- 

 activity, and ultimately 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 tubercles. With the pro- 

 duction 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 

 consists 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 leuco- 

 cytes, all of which are seen in the meshes of the finer 

 fibrous tissues of the part. At the same time altera- 

 tions are produced in the walls of the vessels of the 

 locality ; these tend to occlude them, and thus the proc- 

 ess 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. 



Modes of Infection. — Experimentally, tuberculosis 

 may be produced in susceptible animals by subcutaneous 

 inoculation, by direct injection into the circulation, 

 by injection into the peritoneal cavity, by feeding of 

 tuberculous material, by the introduction of the bacilli 



22 



