98 VACCINE AND SERUM THERAPY 



of production of the fever is not well understood. It 

 cannot be due to the existence in the tuberculin of 

 a direct thermogenic substance, as in that case normal 

 individuals would be affected in the same way as the 

 tuberculous. It has been suggested that in the case 

 of the old tuberculin the fever is the result of the 

 local inflammation excited around the lesions, but 

 this is doubtful in view of the similar action of the 

 new preparation, which is not followed by any such 

 local effects. Others have suggested that the tuber- 

 culin reaction is a condition of anaphylaxis, but by a 

 series of experiments Besredka has conclusively shown 

 such is not the case. Ehrlich has put forward the 

 following explanation : The normal cells of the body 

 are not affected by this substance, nor are those which 

 form the actual tubercular tissue. Probably the latter 

 are habituated to the poison, as they are in close 

 relation with the bacilli which are constantly giving 

 rise to its formation. There is, however, a zone of 

 cells at a certain distance from the centre of infection 

 which have been only so far affected by the poisons 

 of the bacillus as to be rendered unusually susceptible 

 to their influence. When an injection of tuberculin 

 is administered, an additional quantity of poison is 

 brought into contact with these cells, and they are 

 thus stimulated to react. The reaction takes the 

 form of inflammation — the process by which dead or 

 dying tissues are cast off from the body, as is seen 

 in the separation of a sequestrum or a slough. This 

 explanation is supported by the fact that animals in 



