226 PATHOGENIC BACTERIA. 



are injected into the subcutaneous tissues of rabbits 

 small local abscesses develop in the course of a couple 

 of weeks, showing that the tubercle bacilli are chemotac- 

 tically potent. 



While it is extremely interesting to observe that this 

 chemotactic property exists, it seems to be by some other 

 irritant that most of the lesions of tuberculosis are caused. 

 When the dead tubercle bacilli, instead of being injected 

 en masse into the areolar tissue, are so introduced into 

 the body as by intravenous injection as to disseminate 

 themselves or remain in small groups, the result is quite 

 different, and much more closely resembles that of the 

 action of the living organism. 



Batimgarten, whose researches were made upon minute 

 tubercles of the iris, has shown that the first manifesta- 

 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- 



