186 PATHOGENIC BACTERIA. 



them and make themselves appear to constitute the prim- 

 itive cells. When the irritant substance is produced in 

 considerable quantities, the most delicate cells die first ; 

 and it is not infrequent to find a tubercle rich in leuco- 

 cytes suddenly showing degeneration of these cells, with 

 recurring prominence of the original epithelioid cells. 



It has been taught by some that the giant-cells are 

 produced by the union of the leucocytes, but a careful 

 observation of the role played by these cells will convince 

 one that such an origin for these monstrous cells must be 

 very rare. 



Giant-cells are not always produced, for sometimes the 

 necrotic changes are so violent and widespread as to con- 

 vert the whole cellular mass into a granular detritus of 

 unrecognizable fragments. 



Tubercles are constantly avascular, as would be ex- 

 pected of a process which is a combination of progressive 

 irritation and necrosis. The avascularity may be a fac- 

 tor in the necrosis of the larger tuberculous masses, but 

 it plays no part in the degeneration of the smallest tuber- 

 cles, which is purely toxic. 



Tubercles may be developed in any tissue and in any 

 organ. In whatever situation they occur, space is occu- 

 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 



