42 ACTIVE IMMUNIZATION. 



The last point applies not only to aggressins, but equally to other methods 

 of active immunization. In times of an epidemic, aggressin immunization 

 should never be undertaken. 



When one bears in mind the great advantages derived from the employ- 

 ment of this form of immunization, its extensive use should be expected; 

 especially so as animal experimental work with the most important of infec- 

 tious bacteria: typhoid, cholera (Bail), colon (Salus), dysentery (Kikuchi), 

 staphylococcus (Hoke), has proven it to be of greater or less success. And 

 it is therefore no false prophecy, to say that this method will be employed 

 more and more frequently in the future; particularly for pest, in man, results 

 obtained in animal experimentation by Hueppe and Kikuchi have more 

 than sanctioned its employment. 



Other methods of immunization based upon the Aggressin principles 



have been advocated, but none have attained any practical significance. 



Mention however must, in passing, be made of the work of 



Brieger's Brieger and his co-workers Mayer and Bassenge. Brieger 



Bacterial had made extracts of typhoid and cholera bacilli, in the main 



Extracts, identical with artificial aggressins. As far as his sterilization 



was concerned, he obtained that by filtering the extract through 



the Pukal filter. One should remember that during this procedure many 



important substances are lost, but in spite of this, his results of inoculation 



in man have been most encouraging, and there is a possibility that his method 



may take the place of Wright's or Pfeiffer and Kolle, as the reactions are 



very much milder. 



Entirely different from the extracts of living bacteria are those made 

 from previously killed ones. Neisser and Shiga among others, have immu- 

 nized against half parasites in this manner. This is not surprising as the 

 dead bacter al bodies can be similarly used for this purpose. As a general 

 rule, wherever dead bacterial bodies cannot be used for immunization, their 

 extracts will also be found inefficient. The oldest bacterial extracts in use 

 are the tuberculins. 



