IMMUNITY AGAINST TUBERCULIN PREPARATIONS 6 1 



majority of people become infected with tuberculosis at some time during 

 their life, only a small number show symptoms referable to the disease and 

 the rest undergo spontaneous cure. 



Koch further showed that the injection of tuberculous guinea-pigs with 

 large doses of tubercle bacilli produced rapid death, while frequently re- 

 peated small doses evinced favorable effects upon the site of injection and 

 the general condition of the animals. In this way he proved the beneficial 

 influence which successive inoculations exert upon the primary infection. 



In the employment, however, of dead tubercle bacilli in man for thera- 

 peutic purpose a serious difficulty presented itself. It was found that the 

 inoculated dead bacilli were not absorbed, but remained for a long time 

 at the seat of the inoculation instigating suppurative processes. On intra- 

 venous application, formation of tubercular nodules was noticed. 



Koch realized that these harmful effects were due to the non-absorbable 

 parts of the tubercle bacilli; in the main the bacterial capsules. He there- 

 fore attempted to extract the immunizing substances, and in this way 

 brought about the old tuberculin. 



It may be questioned, whether this old tuberculin is identical with tuberculous 

 antigen; whether it is a feasible preparation for purposes of immunity; whether 

 it contains all the important elements of the tubercle bacillus; if not, which are 

 lacking? The specificity of immunity reactions has already been dealt with 

 sufficiently to make it clear that immunizing a healthy individual with old tuberculin 

 will bring about an immunity only against the substances contained within this prepa- 

 ration. That that does not meet the requirement is proven by the fact that an animal 

 immunized against tuberculin will not be protected against a later infection with living 

 tubercle bacilli. It cannot therefore be expected that immunization of a tuberculous 

 individual with old tuberculin will protect him against living tubercle bacilli. The 

 expectation, however, that his immunity will be raised against old tuberculin only, is 

 fully justified. 



Furthermore, we have seen in the aggressin experiments, that inoculation of animals 

 with the aggressin antigen was sufficient to increase the immunity so that a subsequent 

 infection was not attended by any harmful effects. In this case the injected living 

 bacteria are not destroyed, but their ill effects upon the immunized organism have been 

 paralyzed. In other words, the parasites have been transformed to saprophytes, 

 That a similar state of affairs exists in the use of antitoxic sera will readily be seen. 

 The antitoxic diphtheria serum, for example, neutralizes the toxin and thus cures the 

 disease. The bacteria themselves, however, remain intact and also infectious for 

 untreated individuals. Only later on are they absorbed by the phagocytes. When 

 therefore in an individual who has passed through a course of tuberculin treatment 

 there are found fully virulent tubercle bacilli in the sputum, it is no proof, if that is to 

 be the only corroborative evidence, that the tuberculin treatment had been ineffi- 

 cient. In fact, there are strong possibilities that the tubercle bacilli have become 

 transformed into saprophytic bacteria. It is, however, a noteworthy and impor- 

 tant fact, that immunization with tuberculin proves no protection against later 

 infection with living tubercle bacilli, while in the case of aggressins and toxins this 

 is possible. 



