556 IMMUNITY 



practicable method but, like the others, it should not be 

 undertaken without a realization of the possible unfavorable 

 outcome. 



Since the i8th century there has been practiced in France 

 on a large scale the artificial immunization of sheep by the 

 inoculation of the virus of sheep pox just as the variolization 

 of man was practiced before the discovery of small pox vaccine. 

 In France, the law requires the inoculation (clavelization) of 

 flocks in which sheep pox appears, but it interdicts the prac- 

 tice in unattacked flocks. 



2. The injection of animals with attenuated cultures of 

 the bacteria of the disease against which immunity is to be 

 established. This method is used most extensively in 

 anthrax, rabies, symptomatic anthrax, swine erysipelas and 

 bovine tuberculosis. 



The practical value of vaccination for rabies, over that of 

 most other diseases, is the fact that it is effective if made early 

 in the period of incubation. This vaccination taking advant- 

 age of the long period of incubation in rabies, constitutes a 

 form or type of handling of an infectious disease intermediate 

 between protective inoculation and a therapeutic method of 

 treatment. 



Many efforts have been made to procure a vaccine for 

 tuberculosis. Pearson, of the University of Pennsylvania, and 

 von Behring of Marburg, Germany, have done the most work 

 along this line. A number of other workers have reported 

 results, among whom de Schweinitz, Trudeau, M'Fadyean 

 and Schiitz may be mentioned. 



The bovo-vaccine of von Behring consists of living human 

 tubercle bacteria. The results reported by von Behring and 

 others who have tried his vaccine are, for the greater part, 

 encouraging, but as yet the method is in the experimental 

 stage. 



II. Passive immunity. This consists of a temporary im- 

 munity produced by the injection of the blood serum of an 

 animal that has been immunized to the disease. It is em- 



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