CHAPTER VI. 

 THE TUBERCULIN THERAPY. 



Right at the beginning it must be made clear, that tuberculin is not to 

 be considered as a curative agent against tuberculosis, but rather in the 

 light of a bacterial extract for active immunization. In the previous chapter 

 it has been shown that while there are some infectious diseases where im- 

 munization can be accomplished by the use of bacterial extracts and dead 

 bacteria, there are others where immunization is possible only when living 

 vaccines or aggressins of living bacteria are employed. In both of these 

 instances, however, healthy individuals are being treated to be protected 

 from future infection. An exception is presented by rabies. In this dis- 

 ease, the vaccination against the active symptoms is instituted after the 

 infection has already taken place, but the redeeming feature about its 

 treatment is the existence of the very long incubation period. Thera- 

 peutic use of tuberculin, however, is a form of active immunization which 

 belongs to neither of the above classes. The principle involved here is 

 entirely different, and the question arises if it is at all possible to obtain an 

 active immunity by the injection of an antigen in a condition where infec- 

 tion has already taken place, and produced pathological changes. [In 

 other words, where spontaneous immunization has failed.] 



An answer to this question is to be found in Koch's fundamental ex- 

 periments which have been the basis as well as starting point of the entire 

 tuberculin study. 



If a normal guinea-pig is inoculated with tubercle bacilli, the point of inoculation 

 very soon closes. After ten to fourteen days there appears at this site a small hard 

 nodule which finally ulcerates. This shows no tendency to heal and remains so until 

 the death of the animal. If, however, an already tuberculous guinea-pig is similarly 

 inoculated, while the point of inoculation also closes, no indurated nodule appears. 

 Instead, a necrotic process of the skin sets in after the second day, which finally 

 terminates in the casting off of the slough and the formation of a flat ulceration that 

 heals rapidly. It does not matter whether living or dead tubercle bacilli are used 

 for the second infection. 



In explanation of the above phenomenon it must be said that although 

 the first injection had a fatal effect upon the animal, it must have stimu- 

 lated certain immune reactions within the organism which became manifest 

 after the second inoculation. That a condition similar to this, or even 

 more favorable exists in man, is proven by the fact that while the large 



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