CHAPTER VI. 

 THE TUBERCULIN THERAPY. 



Right at the beginning it must be made clear, that the use of 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 immunization 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 disease, 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 antigen in a condition where infection 

 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 experi- 

 ments which have been the basis as well as starting point of the entire tuber- 

 culin 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 at all whether living or dead tubercle bacilli are used for the second 

 infection. 



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

 injection although it had a fatal effect upon the animal must have stimulated 

 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 majority 



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