PATHOGENIC BACTERIA. 29! 



millet-seed. In sections of the tissue young tubercles are 

 found to present several different structures. Near the 

 center, one or more very large cells called giant-cells occur. 

 They contain several or many nuclei which are frequently 

 arranged in a crescentic manner at one side of the cell. 

 Tubercle bacilli can sometimes be demonstrated inside of the 

 giant-cell. Except possibly in the very youngest tubercles, 

 a small area of necrotic tissue will always be found at the 

 center of the tubercle. 



Around the giant-cells and the necrotic area are seen 

 large cells with distinct nuclei which resemble epithelial 

 cells, and are often called epithelioid cells ; they are also 

 often termed granulation cells, and represent an attempt 

 at the formation of granulation tissue. But no new-formed 

 blood-vessels, such as are found in granulation tissue as a 

 rule, occur in the tubercle. Tubercle bacilli may also be 

 found among the epithelioid cells. Outside of these epithe- 

 lioid cells is another layer of small cells called lymphoid 

 cells which represent leucocytes that have appeared in this 

 situation as a part of the inflammatory reaction excited by 

 the presence of the tubercles. The zone of lymphoid cells 

 may be very indistinct or wanting. Frequently it may be 

 very difficult to make out that the cells are arranged in 

 distinct zones at all. The cells are imbedded in a matrix 

 consisting of the connective tissue originally belonging to 

 the part, to which some fibrin may be added. In addition 

 to the fact that no new blood-vessels are formed to main- 

 tain the nutrition of these newly-formed cells, the small 

 vessels included in the tubercle and around it suffer from 

 inflammatory changes. Owing to these causes and to a 

 toxic substance formed by or in the tubercle bacilli, de- 

 generative changes and necrosis take place at the central 

 part of the tubercle. As a result of these degenerative 

 changes the center of the tubercle becomes converted into 

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