290 MANUAL OF BACTERIOLOGY. 



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. Tuber- 

 cle 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 epitheUal cells, and are 

 often called epithelioid cells; they are also often termed granu- 

 lation cells, and represent an attempt at the formation of granu- 

 lation tissue. But no new-formed blood-vessels, such as are 

 found in granulation tissue as a rule, occur in the tubercle. 

 Tubercle baciUi may also be found among the epithelioid cells. 

 Outside of these epithehoid cells is another layer of small cells 

 called lymphoid cells, which represent leukocytes that have 

 appeared in this situation as a part of the inflammatory reaction 

 excited by the presence of the tubercles. The zone of lymph- 

 oid cells may be very indistinct or wanting. Frequently it 

 may be very difficult to make out that the cells are arranged iii 

 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 maintain 

 the nutrition of these newly formed cells, the small vessels 

 included in the tubercle and around it suffer from inflam- 

 matory changes. Owing to these causes and to a toxic sub- 

 stance formed by or in the tubercle bacilli, degenerative 

 changes and necrosis take place at the central part of the tuber- 

 cle. As a result of these degenerative changes the center of 

 the tubercle becomes converted into a dry, yellowish-white, 

 friable mass, resembling dry cream-cheese. Such material 

 is said to be caseous, and the process is called caseation. Prud- 

 den and Hodenpyl found that the injection of dead tubercle 



