THE TUBERCLE BACILLUS 195 



fortunately the great hopes at first entertained have not been 

 realized. A certain number of cases of increased resistance and 

 clinical cures have, however, been reported from its use as a 

 therapeutic agent. 



The tuberculin reaction is local, focal, and general. The local 

 reaction appears as an inflammatory condition at the point of 

 inoculation. The focal reaction consists of an increased blood 

 supply around the infected area and a consequent softening of 

 the focus and a liberation of toxic products which give rise to the 

 general reaction. 



If the dose of tuberculin is not too large the focal reaction soon 

 subsides, with the result that increased cellular activity has caused 

 a further proliferation of connective tissue and fortified the wall 

 surrounding the tuberculous process. In chronic lesions of the 

 bones or inactive skin or ear cases, in which the body cells are only 

 feebly active in self-defense, small doses of tuberculin are reported 

 to have a stimulating beneficial effect. Should the dose of tuber- 

 culin be too large or the body cells incapable of reacting, the focal 

 reaction may be a softening and breaking down of the lesion with 

 liberation of the bacilli and spread of the tuberculous area. Thus 

 tuberculin as a therapeutic agent is a somewhat dangerous weapon. 

 Its success appears to rest upon administering just the right amount 

 to call forth sufficient response without overtaxing the already 

 sensitized body cells. 



Tuberculin as a Diagnostic Agent. The allergic or hypersen- 

 sitive state of the tissue cells in tuberculous individuals makes 

 possible the use of tuberculin as a diagnostic agent, although the 

 phenomenon is as yet little understood. 



A number of tuberculin preparations have been employed. 

 The following is the method originally employed by Koch and 

 usually designated " O.T." A six-weeks-old culture of tubercle 

 bacilli in 5 per cent glycerin broth is killed by heat, filtered, and 

 evaporated down to one tenth of its original volume. The resulting 

 fluid thus contains the products of disintegrated bacilli, substances 

 formed from the medium during their growth and the medium 

 itself. 



