86 BACTERIOLOGY 



Advantage is taken in this method of the relative 

 immunity to infection by other than the usual route of 

 infection. The avenue of infection in this disease is 

 the intestinal tract. By subcutaneous injection of 

 virulent cholera germs a local reaction is produced with 

 slight constitutional disturbances, which, however, is 

 sufficient to produce immunity to the disease. 



Inoculation with Living Bacteria of Attenuated Viru- 

 lence. In this method of securing immunity the viru- 

 lence of the causative germ is diminished by various 

 procedures, as by cultivating them in the presence of 

 antiseptics, as in anthrax; by cultivating in high tem- 

 perature, also used for anthrax vaccines; by drying, as 

 in vaccination for hydrophobia; by passing through an 

 unfavorable host, as in small-pox vaccination. Im- 

 munization for anthrax in animals and for small-pox in 

 man are examples of this form of active immunization. 



Inoculation with Dead Bacteria (Bacterial Vaccines). 

 This method of securing immunity is the most prac- 

 tical and of the widest application of perhaps all the 

 methods of securing active immunization. In connec- 

 tion with the use of the opsonic index it is becoming of 

 increasing importance in the prevention of bacterial 

 disease. The most important example of this form of 

 immunization in man is in the vaccination against ty- 

 phoid fever. It is also used in vaccination against chol- 

 era and plague. 



Inoculation with Bacterial Toxin. This method of 



