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ACTIVE IMMUNIZATION 



Following this discovery, much work was done, for it appeared that 

 the question of prevention of any bacterial disease simply depended 

 upon whether the bacterium could be cultivated and so modified or 

 attenuated that while its injection would not be followed by disease or 

 other harmful effects, it would be capable of causing the production of 

 specific antibodies. 



Naturally, most of the earlier work was done with the infections of 

 the lower animals, and, consequently, most discoveries were directly 

 beneficial to them. Pasteur soon devised a method of attenuating 

 anthrax bacilli by exposing them to certain temperatures for varying 

 lengths of time, so that a vaccine could be prepared that has proved of 

 great value. Later the same observer discovered a method of attenuat- 

 ing the virus of hydrophobia by a process of drying, and devised a 

 practical method of prophylactic immunization against this disease. 

 In addition to these his vaccines against swine erysipelas, symptomatic 

 anthrax, and rinderpest have become well known. 



The knowledge gained from a study of the diseases of the lower ani- 

 mals and the aid given them has been applied to human medicine with 

 considerable benefit, not only in prophylactic immunization, but also 

 in therapeutics (bacterin therapy). The latter application is a more 

 recent discovery, for wnich we are mainly indebted to the researches 

 of Wright, Leishman, Douglas, and their colleagues. 



Nomenclature. The word vaccine is from the Latin vacca (a cow). 

 Cowpox was called "vaccinia," or the cow disease, and Jenner designated 

 protective inoculation against smallpox with cowpox virus as vaccination. 

 With true courtesy Pasteur adhered to Jenner's nomenclature and 

 applied the term vaccine to emulsions of dead or attenuated bacteria. 

 This is unfortunate and tends to create confusion, as the term vaccine 

 is inseparably associated with cowpox virus or lymph. The term bac- 

 terial vaccine has become widely known, and is used to designate bacterial 

 suspensions prepared for purposes of immunization. There is no essen- 

 tial difference, however, between cowpox vaccine, which contains the 

 modified germ or virus of smallpox in a diluent of lymph, and a bacterial 

 vaccine containing the germ, modified by some physical or chemical 

 agency in a diluent of saline solution or bouillon. It is, however, well 

 to reserve the unqualified term " vaccine" for cowpox virus, and to 

 retain the designation "bacterial vaccine" for suspensions of attenuated 

 or dead bacteria. More recently the term bacterin has been applied 

 to the latter, but this would imply an extract of bacteria, as, e. g., tu- 

 berculin, which is not always the case. 



