SPECIFIC BACTERIAL REACTIONS 175 



toms as they are eliminated. The focal reaction con- 

 sists of the fresh inflammatory changes noted at the 

 tuberculous focus, namely, congestion, pain, tender- 

 ness, swelling, redness, etc. The local reaction com- 

 prises the inflammatory signs observed at the site of 

 the injection. The focal and local reactions are ex- 

 plained by the interaction of combined tuberculin, 

 newly formed antibodies and complement, in attract- 

 ing phagocytes, with direct localizing action, produc- 

 ing thereby an inflammatory reaction. If the local 

 reaction be severe, necrotic tissue may be cast off. 

 Following the above reactions, there is a tendency ex- 

 hibited by the pathological process to heal. 



Tuberculin as a Diagnostic Agent. — The employ- 

 ment of tuberculin in a diagnostic capacity is very ex- 

 tensive, and rightfully so, because, properly and com- 

 petently utilized, its value at times as an aid in 

 difl*erential diagnosis is inestimable. In the authors' 

 experience the positive or negative information thus 

 yielded has been absolutely dependable. Its proper 

 use, however, entails the greatest caution and dis- 

 crimination as to indications and contra-indications on 

 the part of the patient, size and administration of 

 doses, and, not least of all, the correct brand of tuber- 

 culin. Unanimity of opinion prevails that Koch's old 

 tuberculin, " O. T.," whatever may be its method or 

 form of application, is best for diagnostic purposes. 



