170 ANTIGENS AND THE TECHNIC OF SERUM REACTIONS 



forth by Wright marks a distinct epoch in bacterial therapeutics in 

 spite of the practical failure of his opsonic index determination as 

 a theoretical guide to immunization and treatment. He has used 

 bacterial vaccines both for prophylaxis to prevent infection with 

 specific bacteria and therapeutically to arrest infection. 



Prophylactic Vaccination. The object of prophylactic vaccination is 

 to increase the resistance of the recipient to specific infection. This 

 is accomplished by reinforcing the natural initial defenses of the 

 body with specific antibodies, generated in the host in response to 

 the injection of the specific microorganism as a vaccine. In prophy- 

 lactic vaccination the host has ample time to work over the vaccine, 

 and by prolonging the treatment through repeated graduated doses 

 the maximum degree of immunity may be expected. To attain the 

 maximum immunizing effect the bacteria of the vaccine should be as 

 near their normal state as possible, that is, they should be endowed 

 with all the antigenic properties they possess in the natural disease 

 produced by them in the host. 



Following the brilliant work of Jenner with cowpox vaccine and the 

 epoch-making observations of Pasteur, observers are fairly agreed 

 that the best results from prophylactic vaccination are obtainable 

 only by the use of an attenuated living virus. The action of such a 

 living virus is, as Theobald Smith 1 has aptly expressed it, " a multitude 

 of feeble blows, each of which produces an immunological response." 

 The dangers attending the use of attenuated viruses, however, ordi- 

 narily preclude their employment, due to inability to control the 

 virulence of attenuated cultures. The possibility of creating carriers 

 cannot be overlooked. For this reason killed cultures are almost 

 invariably selected. 



It is, of course, impossible to utilize an autogenous vaccine, but 

 for purposes of immunization a polyvalent vaccine is indicated. The 

 action of a dead virus is limited practically to a single immunological 

 response, hence the need of repeated inoculations. 



Therapeutic Vaccination. In chronic, long-drawn out focal or local 

 infections, the invading microbes are either holding their own or 

 gaining the ascendency and the object of bacterial vaccination is to 

 turn the tables on the invaders. The products of immunization must 

 be used at once, and the organisms comprising the vaccines for this 

 purpose cannot ordinarily be as resistant as their originals in the host. 

 The underlying principle of therapeutic vaccination, according to 



1 Jour. Am. Med. Assn., 1913, Ix, 1591. 



