150 THE MORE CHRONIC INFECTIOUS DISEASES 



some of the smaller air tubes, and extends into adjoin- 

 ing lung tissue by continuity. It may enter the lungs 

 by following the lymph way, or it may get there from 

 the blood stream or lymph when it has been taken 

 into the intestines in food or drink. These bacteria 

 can pass through a mucous membrane into the deeper 

 tissue without leaving any inflammation at their 

 point of entry. After having entered the tissues proper 

 they may be carried anywhere by the lymph and 

 probably by the blood. 



Tubercles. Having settled at a point of low resist- 

 ance, they irritate the tissue rather slowly to produce a 

 localized inflammation which is called a tubercle, a 

 gray body about the size of a millet seed. The cells 

 composing this little mass are very much the same 

 as those seen in chronic local non-tuberculous inflam- 

 mations, but their arrangement, particularly when 

 combined with large cells having numerous nuclei 

 about their edge (giant cells), is rather characteristic 

 of the disease. Many of these tubercles spread centri- 

 fugally and coalesce. The centre of the tubercles, 

 being devoid of nutriment, since the blood supply is 

 cut off, undergoes cheese-like or caseous softening. 

 The combination of many tubercles and their destroyed 

 centre produces large caseous abscesses. When these 

 are in the lungs the softened centres may be removed 

 by being coughed up after the process has ulcerated 

 into an air passage. In the kidney the same general 

 thing may occur, and the softened matter goes into 

 the urine. 



Forms of Tuberculosis. When the process ulcerates 

 into the blood supply there may result a rapid dissemi- 



