BACTERIAL VACCINES. 65 



ially to the efforts of Wright. It is important to note that the 

 method of vaccination was used by Wright before he had dis- 

 covered opsonins. From his later observations Wright has decid- 

 ed that opsonins are of the utmost importance in immunity to 

 some organisms, and are decreased in amount during most infect- 

 ions but that they can be increased by the injection of bacterial 

 vaccine. 



BACTERIAL VACCINES. 



It was stated in a former chapter that in bacterial infections 

 the infected body absorbs bacterial substances and products. 

 According to the amount of substance and products absorbed 

 immune substances are produced. When much is absorbed suf- 

 ficient immune substance is usually produced to cure the disease, 

 but when little is absorbed not enough immune body is produced 

 to cure the infection which then becomes chronic. To produce 

 enough immune substances to affect a cure from an infection 

 Wright and Douglas have employed the well known principle of 

 active immunization. The method they have suggested is to 

 actively immunize by injection at the proper time, of proper doses 

 of killed Cultures of the organisms causing the infection. The 

 effects of injection of killed cultures or vaccines according to these 

 investigators is to produce certain changes in the opsonin content. 

 Wright and Douglas attempt to immunize by giving injections 

 of such numbers of bacteria as will produce only a slight negative 

 phase which lasts only a short time and is followed by a rise in 

 opsonic index which lasts for some days. When the index begins 

 to fall after the subsidence of the positive phase, another injec- 

 tion is made and the effect on the opsonic index is determined. 

 An attempt is made to inject such doses at the second and sub- 

 sequent injection that there shall again be only a slight negative 

 phase and that during the positive phase the opsonic index shall 

 be higher than following the first injection. An effort is made to 

 keep the opsonic index of the individual above normal. If the 

 index shows a marked drop after any injection, the dose has been 

 too large. By means of vaccines Wright claims that the anti- 

 bacterial power of the blood can be increased for any microbe 

 invading the body. In 1906 Wright was able to say that he had 

 by this method achieved uniform success. 



