244 



THE INFECTIOUS DISEASES. 



Blood-vessels are not apt to develop under the influence of the tubercle 

 bacillus. Old blood-vessels are, ou the other hand, usually obliterated 

 as the new tissue forms. 



Sooner or later, under the influence of the tubercle bacillus, there is 

 usually a damage of cell and tissue, which may lead to coagulation necro- 

 sis in the new-formed as well as in the old tissue of the infected region. 

 This necrosis is more apt at first to manifest itself in the central portions 

 of the tuberculous foci (Fig. 119) and may progress outward; the nuclei 

 become fragmented or disappear, or fail to stain in the usual way, the 



Fro. 119. A MILIARY TUBERCLE IN THE LUNG. 

 Showing polyhedral cells, small spheroidal cells, and giant cells, with coagulation necrosis at the centre. 



protoplasm becomes more homogeneous, and cells and stroma form at 

 last an irregularly granular mass of tissue detritus which tends to disin- 

 tegrate (coagulation necrosis, cheesy degeneration, caseation), forming 

 cavities or, if on free surfaces, ulcers. 



As coagulation necrosis progresses, the tubercle masses lose the gray 

 translucent appearance which in their early stages they are apt to pre- 

 sent to the naked eye and become more opaque and of yellowish-white 

 appearance at the centres. 



Finally dense fibrous tissue may form in and about foci of tuberculous 

 inflammation, encapsulating or sometimes entirely replacing the more 

 characteristic new-formed structures. It is in this way by the forma- 

 tion of connective tissue that such repair as is possible after local tuber- 

 culous inflammation, is brought about (Fig. 289, p. 508). 



