228 PATHOGENIC BACTERIA. 



pied at the expense of the tissue, whose component cells 

 are pushed aside or else included in the nodule. In mil- 

 iary tuberculosis of the kidney it is not unusual to find a 

 tubercle including a whole glomerule, and resolving its 

 component thrombosed capillaries and epithelium into 

 necrotic fragments. 



As almost all tissues contain a supporting tissue-frame- 

 work of connective-tissue fragments, some of these must 

 be embodied in the new growth. The fibres which pos- 

 sess little vitality are more resistant than cells, and, after 

 all the cells of a tubercle have been destroyed, will be 

 distinctly visible among the granules, so that the tubercle 

 has a reticulated appearance. 



As a rule, tubercles steadily increase in size by the in 

 vasion of fresh tissue. The tubercle bacillus does not seem 

 to find the necrotic centres of the tubercles adapted to its 

 growth, and completes its life-cycle with the tissue-cells. 

 It is unusual to find healthy-looking bacilli in the necrotic 

 areas, most of them being observed at the edges of the 

 tubercle, where the nutrition is good. From such edges 

 the bacilli are occasionally picked up by leucocytes and 

 transported through the lymph-spaces, until the phago- 

 cyte falls a prey to its prisoner, dies, and sows the seed 

 of a new tubercle. However, for the spread of tubercle 

 bacilli from place to place phagocytes are not always 

 necessary, for the bacilli seem capable of transportation 

 by streams of lymph alone. 



Notwithstanding the steady advance which takes place 

 in most observed cases of tuberculosis, and the thoroughly 

 comprehensible microscopic explanation of it, many cases 

 of tuberculosis make quite perfect recoveries. 



The periphery of every tubercle is a zone of reaction, 

 with a marked tendency to granulation and organization. 

 If the vital condition is such that through inappro- 

 priate nutriment or through unusually active phago- 

 cytosis the activity of the bacilli is checked or their 

 death is brought about, this tendency to cicatrization is 

 allowed to progress unmolested, and the necrosed mass is 



