BACTERIUM TUBERCULOSIS 139 



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

 ing lung tissue by continuity. It may get into the 

 lungs by following the lymph way, or as has lately 

 been proven, 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 any- 

 where 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. This 

 is usually 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 

 inflammations, but their arrangement, particularly 

 when combined with large cells having numerous 

 nuclei about their edge (giant cells), is rather character- 

 istic of the disease. Many of these tubercles spread 

 centrifugally 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- 



