238 TEXT-BOOK OF BACTERIOLOGY. 



but we will see at the same time a series of histologically striking' 

 changes in the tissue, long regarded as characteristic of tubercu- 

 losis. This affection produced, in the first place, a new growth, 

 appearing mostly in the form of those small, grayish-white, trans- 

 parent tubercles from which the disease derives its name and 

 which were called by Cohnheim " infection tumors " according to 

 their origin and kind. The tubercle is composed of an accumula- 

 tion of round cells similar to lymph-corpuscles; besides, there are 

 more or less numerous, somewhat larger, so-called epithelioid cells 

 and also some giant cells lying in the middle or near the edge. The 

 bacilli are especially abundant in these latter (but are also found 

 outside of them), and there can be no doubt that the entire forma- 

 tion is caused by the action of the bacteria. 



We do not yet positively know how this is produced. While it 

 had formerly been supposed that emigrated white blood- corpuscles 

 had exclusively formed the tubercle and had then united with epi- 

 thelioid and giant .cells, Baumgarten has assigned an important 

 function to the cells of connective tissue and of epithelial origin. 

 The bacilli coming in contact with these cells excite an irritation, 

 which results in a proliferation of the cells to the extent of a division 

 of the nuclei. But this irritation is not sufficient to cause the for- 

 mation of an entire new cell. Hence there remains only the former 

 division, and a giant cell is, according to Baumgarten, not formed 

 by the union of several epithelioid cells, but by a simple germ divi- 

 sion. The "epithelioid -cell tubercle" is developed, after which, 

 under the influence of continued irritation, migration of white blood- 

 corpuscles from the vessels takes place, changing the epithelioid 

 into a lymphoid-cell tubercle. 



The series of changes is not yet completed. A process takes 

 place in the interior of the giant cells, an accurate description of 

 which we owe to Weigert. Here the bacilli present produce a de- 

 generation or coagulation necrosis, especially in the middle of the 

 tubercle. The result is a uniformly dull, non-nucleated mass which 

 the anilin colors do not stain. This mass consists of degenerated, 

 practically necrotic cells, and very soon the bacilli disappear from 

 it. But frequently we find in the same giant cell, the interior of 

 which has undergone a retrograde change, a plentiful nuclear 

 division resulting in the progressive development of tissue resem- 

 bling granulation tissue in which are found large numbers of 

 tubercle bacilli. 



Thus we have here in both of those processes which are charac- 

 teristic of the tubercular process, neoplasm (production of tissue 

 on one hand) and retrogressive metamorphosis (destruction of tis- 



