56 THE TUBERCULIN THERAPY. 



of people become infected with tuberculosis at some time during their lives, 

 only a small proportion show symptoms referable to the disease and the 

 other greater number undergo spontaneous cure. 



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

 large doses of tubercle bacilli produced rapid death, while frequently repeated 

 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 the purpose 

 of therapeutic injections, 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 

 intravenous application, formation of tubercular nodules was noticed. 



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

 parts of the tuberc'e bacilli; in the main the bacterial capsules. He therefore 

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

 about the existence of old tuberculin. 



Questions may here be asked to the effect, whether this old tuberculin is identical 

 with tuberculous antigen; whether it is at all a feasible preparation for purposes of 

 immunity; does it contain all the important elements of the tubercle bacillus, if not 

 which are lacking? The specificity of immunity reactions has already been dwelt upon 

 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 borne out. 



Furthermore, we have seen that in the aggressin experiments, 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 the only corroborative evidence, 

 that the tuberculin treatment had been inefficient. In fact, there are strong possibilities 

 that the tubercle bacilli have become transformed into saprophytic bacteria. It is, how- 

 ever, a noteworthy and important 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. 



Although tuberculin cannot be considered as the aggressin or toxin of the 

 tubercle bacilli, it simulates these substances with sufficient closeness to 



