PROTECTIVE IMMUNIZATION AMONG THE LOWER ANIMALS 653 



itself, such inoculations may, however, prevent a severe attack of the 

 disease by producing some immunity against secondary streptococcic 

 infections. 



PROTECTIVE IMMUNIZATION AMONG THE LOWER ANIMALS 



Since discoveries in bacteriology and immunity have usually been 

 intimately associated with animal experimentation, it is not strange 

 that the lower animals should have been the first to benefit from the 

 knowledge thus gained. As a consequence, vaccine therapy, both 

 prophylactic and therapeutic, is being extensively used in veterinary 

 practice with good results. 



ANTHRAX 



This was one of the first vaccines studied by Pasteur, and as a prophy- 

 lactic measure, it has proved of great value. It finds its greatest field 

 of usefulness in case of an outbreak of anthrax, when it is used to pro- 

 tect the uninfected members of a herd, as well as any animals pasturing 

 on infected areas. 



In preparing the vaccine Pasteur was hampered by the fact that the 

 spores of anthrax bacilli retain the virulence of the original bacilli. As 

 the result of extended experiments, however, he discovered a means of 

 attenuating the virulence of cultures by growing the bacilli at a tem- 

 perature of 42 C.; he also found that inoculation with these attenuated 

 bacilli would effectively vaccinate sheep and cattle, and so protect them 

 against an attack of the disease. 



One of the most dramatic stories 1 in the history of science is the 

 account of the method by which Pasteur demonstrated his discovery to 

 the public. Certain harsh critics, having heard of Pasteur's ability to 

 prevent anthrax in laboratory experiments, and anxious to humiliate 

 him, sent him a public challenge to demonstrate the experiment on a 

 practical scale at a farm in the country. A number of farmers offered 

 to place 60 sheep at his disposal. The challenge was immediately 

 accepted, and Pasteur mapped out a plan of action, in which he safe- 

 guarded himself by making no half-statements, but boldly promised 

 complete success. Of the total number, 25 sheep were to be vaccinated 

 and 25 were to remain un vaccinated. A fortnight later all 50 were to 

 receive a lethal dose of the fully virulent anthrax. He declared that 

 the 25 non-vaccinated sheep would die, whereas the 25 vaccinated would 

 remain alive and well. The remaining 10 sheep were to serve as controls. 

 1 Narrated by Elizabeth Fraser. 



