tiEROTHERAPEUTIC MEASURED. 363 



organisms into a tissue which has some natural re- 

 sistance. The success of vaccination against small- 

 pox by using virus obtained directly from the dis- 

 eased, a method which was practiced in earlier 

 times, was probably due to the fact that the virus 

 found unfavorable conditions for the development 

 of virulence in the skin. In some instances im- 

 munization is accomplished more successfully by 

 inoculation of bacteria or toxins into the blood 

 stream, as in Kitt's method of vaccination against 

 symptomatic anthrax and in immunization with 

 rattlesnake venom. 



2. Injection of attenuated virus or toxin. At- 

 tenuation may be accomplished by air and light 

 (chicken-cholera, Pasteur) ; by cultivation at high 

 temperatures (anthrax, Pasteur) ; by chemical 

 agents (anthrax, Eoux; diphtheria and tetanus 

 toxins, Behring and Eoux) ; by desiccation (rabies, 

 Pasteur) ; by passing the virus through other 

 animals (swine erysipelas, Pasteur). This last 

 observation was a most instructive one; passing 

 the bacillus through the rabbit several times in- 

 creased its virulence for the rabbit but decreased it 

 for swine, while passing the organism through the 

 dove increased its virulence for swine. 



3. Injection of killed organisms (anthrax, Tous- 

 saint; swine plague, Salmon and Smith). This 

 is the safest means of vaccinating against cholera, 

 typhoid and plague. In the Pasteur treatment of 

 hydrophobia the first injection of the dried spinal 

 cord probably contains the killed virus. 



4. Injection of bacterial constituents (a) Bacter- 

 ial cell plasm (Buchner's plasmin, obtained by sub- 

 mitting micro-organisms to high pressure, and 

 Koch's tuberculin TE) ; (&) Soluble bacterial 



