668 ACTIVE IMMUNIZATION 



cerned in producing necrosis, but likewise the protein constituents 

 responsible for specific sensitizing action and anaphylactic disturbances. 

 For example, tuberculocidin and tuberculol are examples of attempts at 

 isolating the pure immunizing principle; endotin, or Moeller's tuber- 

 culin, is an example of an endeavor to rid the culture fluid of protein 

 substances. 1 



Action of Tuberculin. If a healthy or a tuberculous individual is 

 injected with old tuberculin, an immunity will be established only 

 against the substances contained in this preparation. That this does 

 not fulfil the requirements is proved by the fact that an animal im- 

 munized against this tuberculin will not be protected against a later 

 infection with living tubercle bacilli. It was mainly for this reason 

 that tubercle emulsion and new tuberculin were devised and used, in 

 the effort to provide immunization not only against the products of the 

 bacilli, but against the bacilli themselves, and to bring about their actual 

 destruction. 



Probably none of the various tuberculins can be considered as re- 

 presenting the true toxins of the tubercle bacillus, although they simu- 

 late these substances with sufficient closeness to bring about partial 

 immunity against some of the poisonous products and to warrant their 

 use in tuberculosis. An individual may become immunized against old 

 tuberculin so that large doses will evoke no reaction, but this does not 

 necessarily imply that a cure has resulted; in fact, the injection of another 

 preparation, such as new tuberculin or bacillus emulsion, may bring 

 about a reaction. 



Partial immunization possesses, however, distinct advantages, in 

 that it lessens some of the symptoms of tuberculosis. In addition, 

 tuberculin immunization may give most important aid in walling off 

 tuberculous foci with fibrous tissue, and in this manner bring about a 

 condition of potential cure. Following the injection of tuberculin a 

 focal reaction occurs, characterized by hyperemia and exudation about 

 the diseased tissues. While an excessive dose of tuberculin may produce 

 excessive hyperemia, exudation, and necrosis of tuberculous tissue and 

 lead to actual harm, these being some of the effects that followed the 

 early use of tuberculin and resulted in bringing it into high disfavor, 

 smaller and carefully graduated doses tend to produce a mild inflamma- 

 tory hyperemia leading to destruction of tuberculous tissue and the 



1 For a full account of these and other preparations I refer the reader to the book 

 of Hamman and Wolman, "Tuberculin in Diagnosis and Treatment," 1912, Appleton 

 & Co. 



