Lesions 733 



necrotic changes are sometimes so rapid and widespread 

 as to convert the whole into a mass of unrecognizable frag- 

 ments. 



Tubercles are constantly avascular i. e., in them no 

 new capillary blood-vessels form, as in other inflammatory 

 tissues and the coagulation-necrosis soon destroys pre- 

 existing capillaries; the avascularity may be a factor in the 

 necrosis of the larger tuberculous masses, though probably 

 playing no important part in the degeneration of the small 

 tubercles, which is purely toxic. 



The minute primitive tubercle was first called a miliary 

 tubercle, and small aggregations of these, "crude tubercles," 

 by Laennec. Tubercles may be developed in any tissue 

 and in any organ. In whatever situation they occur, the 

 component cells are either pushed aside or included in the 

 lesion. In miliary tuberculosis of the kidney it is not un- 

 usual to find a tubercle including a glomerule, and resolving 

 its component capillaries and epithelium into necrotic frag- 

 ments. In this way the tissues become disorganized and 

 disintegrated. 



As almost all tissues contain a supporting connective- 

 tissue framework, its fibers must be embodied in the new 

 growth. These possess little vitality, but are more resistant 

 than the cells, and, after the cells of a tubercle have been 

 destroyed, may be distinctly visible among the granules, 

 giving the tubercle a reticulated appearance. 



As a rule, tubercles progressively increase in size by the 

 invasion of fresh tissue. The tubercle bacillus does not 

 seem to find the necrotic centers of the tubercles adapted 

 to its growth, and most of the bacilli are usually observed 

 at the edges, among the healthy cells, where the nutri- 

 tion is good. From this position they are occasionally 

 picked up by leukocytes and transported through the 

 lymph-spaces, until the phagocyte falls a prey to its pris- 

 oner, dies, and sows the seed of a new tubercle. However, 

 for the spread of tubercle bacilli from place to place phago- 

 cytes may not always be necessary, for the bacilli can 

 probably be transported by streams of lymph. It is by 

 the steady advance in necrosis and consolidation that the 

 tissues invaded are destroyed, becoming cheesy and crumbly 

 and forming necrotic masses which, in the lungs, gradually 

 crumble away, the detritus escaping through the air-tubes, 

 thus forming cavities. From the beginning of pulmonary 



