TUBERCULOSIS. 185 



tion of the irritation caused by the bacillus is not the 

 attraction of leucocytes, but the stimulation of the fixed 

 connective-tissue cells of the part affected. These cells 

 increase in number by karyokinesis, and form about the 

 irritating bacterium a minute focus which is the primitive 

 tubercle. 



The leucocytes are of secondary advent, and are no 

 doubt attracted both by the substance shown by Prudden 

 and Hodenphyl to exist in the bodies of the dead bacilli 

 and by the necrotic changes which already affect the 

 primary cells. For reasons not understood, the amount 

 of chemotaxis varies greatly in different cases. Some- 

 times the tubercles will be sufficiently purulent in type 

 almost to justify the name "tubercular abscess;" some- 

 times there will be a marked absence of cellular ele- 

 ments derived from the blood. 



The important toxic substance produced by the bacillus 

 is evidently not associated with chemotaxis, for when the 

 leucocytes are absent the necrosis which is so characteris- 

 tic persists. 



The groups of cells constituting the primitive tubercle 

 have scarcely reached microscopic proportions before a 

 distinct coagulation-necrosis is observable. The proto- 

 plasm of the cells affected takes on a hyaline character, 

 and seems abnormally viscid, so that contiguous cells 

 have a tendency to become partially confluent. The 

 chromatin of their nuclei becomes dissolved in the nu- 

 clear juice and gives stained nuclei a pale but homo- 

 geneous appearance. Sometimes this nuclear change is 

 only observed very late. As the necrosis advances the 

 contiguous cells flow together and form large protoplas- 

 mic masses giant-cells which contain as many nuclei 

 as there were component cells. It may be that these 

 nuclei multiply by karyokinesis after the protoplasmic 

 coalescence, but only one observer, Baumgarten, has 

 found signs of this process in giant-cells. While these 

 changes are in progress in the cells of the primary focus, 

 the leucocytes may collect in such numbers as to obscure 



