TEXT-BOOK OF BACTERIOLOGY. 239 



sue on the other hand). Finally, sooner or later the structure of 

 the tubercle, the infection tumor, undergoes degeneration and per- 

 ishes, the final result being, as a rule, the formation of a tubercular 

 abscess. The blood-supply is shut off, or very greatly impeded by 

 an obliterating endarteritis, which is caused by the proliferation of 

 the endothelial cells lining the vessels. 



The distribution of bacilli in the tissue corresponds to the above 

 facts and conditions. They are seen, in the beginning, lying singly 

 between the cells without the appearance of any other changes. 

 But the first settlement is soon surrounded by the lymphoid ele- 

 ments, which now commence the formation of the real tubercle, and 

 the rods appear at the same time within the cells which have re- 

 ceived the foreign intruders, perhaps with the hopeless view of de- 

 stroying them. If we regard the white blood-corpuscles as precur- 

 sors and preliminary steps in the formation of epithelioid and 

 giant cells, the presence of bacteria in these latter is not remarka- 

 ble. But if, with Baumgarten, we consider that the connective-tissue 

 cells essentially give rise to the histological neoplasm, it is difficult 

 to understand how micro-organisms destitute of voluntary motion 

 can get into the interior of the cells. 



The tubercle bacilli generally occupy a quite characteristic posi- 

 tion in the giant cells. While the centre consists of a non-nucleated 

 region destroyed by coagulation necrosis, there are found at the 

 margin of one side of the cell many nuclei arranged in a wreath, 

 and exactly opposite to them, at the other side of the margin, the 

 rods. This position is by no means regular. Here, too, the pecu- 

 liarities of the different kinds of animals play a part; with the 

 marmot and the Spermophilus guttatus (a rodent very common in 

 southern Russia, which, according to MetschnikofTs investigations, 

 is exceedingly susceptible to infection with tubercle bacilli) the rods 

 also lie in the very numerous giant cells, irregularly scattered and 

 often exhibiting very remarkable forms of degeneration. They are 

 swollen, club-shaped, ^nd change finally into amber-yellow, flaky 

 masses hardly indicating the origin of tubercle bacilli. 



But there are also transition forms met with which are of a 

 peculiar nature. Metschnikoff regards this annihilation of the bac- 

 terial protoplasm as an immediate sequel of cellular activity, and 

 sees in the giant cells even phagocytic elements. 



The bacilli perish in the course of the tubercular process accom- 

 panying the progressive decay and increasing necrosis. Their num- 

 ber is thus frequently small, especially in cases of extensive and 

 radical tubercular changes. The bacteria may, finally, disappear 

 even completely, and leave their traces only in the consequences of 



